Thin film device provided with coating film, liquid crystal panel and electronic device, and method for making the thin film device

ABSTRACT

Any one of an insulating film forming a TFT, a silicon film and a conductive film is formed by applying a solution and annealing it. In a spin coater ( 102 ), a coating solution containing a thin film component which is supplied from a solution storage section ( 105 ) is spin-coated onto a substrate. The substrate after coating the coating solution is annealed in an annealing section ( 103 ) to form a coating film on the substrate. Additional laser annealing improves one of film characteristics, i.e., crystallinity, density and adhesiveness. Application of the coating solution or a resist by an ink jet process increases utilization of the solution and permits forming a patterned coating film. Because a thin film device in accordance with the present invention is inexpensive and has a high throughput, TFT production by a production system having high utilization of the coating solution drastically reduces initial investment and production cost of a liquid crystal display device.

This is a Division of application Ser. No. 09/325,567 filed Jun. 4,1999, which in turn is a Continuation of application Ser. No. 08/983,036filed Feb. 13, 1998, which in turn is a U.S. National Stage ofPCT/JP97/01618 filed May 14, 1997. The entire disclosure of the priorapplication(s) is hereby incorporated by reference herein in itsentirety.

TECHNICAL FIELD

The present invention relates to a thin film device including a thinfilm laminate structure such as a thin film transistor (hereinafterreferred to as TFT) and a method for making the same, and in particularrelates to a thin film device capable of low cost production due to adecreased initial investment and a method for making the same. Also, thepresent invention relates to a liquid crystal panel and an electronicdevice using the thin film device.

BACKGROUND ART

In recent years, liquid crystal display devices using such types of thinfilm devices have been used in notebook-type personal computers, carnavigation systems, video cameras and various portable informationdevices, and their range of applications and production is drasticallyincreasing. Such phenomena are due to improved performance includingreduced price of the liquid crystal display devices, enlarged screensize, improved image resolution and low electrical power consumption.Further cost reduction is, however, required for further expansion ofthe market and range of applications.

The mainstream of the liquid crystal devices is active matrix liquidcrystal devices using TFTs as switching elements for pixels. Each liquidcrystal device includes TFTs, a TFT substrate on which a matrix of pixelelectrodes connected to the TFTs are formed, a counter substrateprovided with a common electrode, and a liquid crystal encapsulatedbetween these two substrates. FIG. 17 shows the main section of a TFTsubstrate 60. In FIG. 17, TFTs 61 are formed at pixel positions near theintersections of a plurality of source or data signal lines S1, S2, . .. Sn arranged in columns with a plurality of gate or scanning signallines G1, G2, . . . Gm arranged in rows. Source electrodes of the TFTs61 are connected to their respective source lines, and drain electrodesare connected to their respective pixel electrodes 62. The data signalsupplied from a source line is applied to a pixel electrode 62 throughits corresponding TFT 61 based on the scanning timing signals suppliedthrough the corresponding gate line. The state of the liquid crystal ischanged and driven for displaying by an electric field between the pixelelectrode 62 and the common electrode, not shown in the drawing.

The liquid crystal display device is fabricated by panel assemblingincluding encapsulation of the liquid crystal between the TFT substrate60 and the counter electrode, and packaging of driving circuits fordriving the source lines and the gate lines. The cost of the liquidcrystal display device greatly depends on the cost of the TFT substrate60. The cost of the TFT substrate 60 depends on the manufacturing methodof the TFTs. A part of driving circuits may be formed on the TFTsubstrate 60 by forming the active elements with the TFTs, and in thiscase, the cost of the TFT substrate represents a high proportion of thecost of the liquid crystal display device.

A TFT has a thin film monolithic structure including a plurality of thinfilms which include at least a silicon semiconductor layer having aninsulating layer, a conductive layer, a source, a drain and a channelregion. The cost of the TFT greatly depends on the production cost ofthe thin film monolithic structure.

The insulation layer in the thin film monolithic structure is formed bya low pressure chemical vapor deposition (LPCVD) process or a plasmaenhanced CVD (PECVD) process, because a normal pressure CVD (NPCVD)process results in low uniformity of the film thickness. The conductivelayer, or typically the metal layer, is formed by a sputtering process.The silicon film for forming the silicon semiconductor layer is alsoformed by the PECVD or LPCVD process. Further, a method for implantingan impurity into the silicon film by an ion implanting process or an iondoping process is used. Alternatively, the high concentration impurityregion which functions as a source-drain region is formed of animpurity-doped silicon film in a CVD system.

The CVD systems and the sputtering system used in the above-mentionedfilm deposition processes belong to vacuum units for processingmaterials under vacuum pressures, and require large vacuum systems,resulting in an increase in initial investment. In the vacuum system, asubstrate is transferred to a vacuum evacuation chamber, a substrateheating chamber, a film deposition chamber and a vent chamber, in thatorder, to form a film. The substrate atmosphere therefore must bechanged from open air to vacuum, and this limits the throughput. Becausethe ion implanter and the ion-doping system are also vacuum systems, thesame problems as above occur. Further, the ion implanter and theion-doping system require complex mechanisms for generating plasma,extracting ions, mass-separating the ions (for the ion implanter),accelerating ions, collimating ions, scanning ions and so on, resultingin a remarkably high initial investment cost.

As described above, the thin film deposition technology and theprocessing technology for producing a thin film monolithic structure arebasically similar to the manufacturing technology for LSI circuits. Themain means for cost reduction of the TFT substrate include scaling-up ofthe substrate size for forming TFTs, improvement in efficiency of thethin film deposition and its processing step, and improvement in yield.

Scaling-up of the substrate size for producing large liquid crystaldisplay devices with reduced costs is an obstacle to high speed transferof the substrates in the vacuum system, and causes breakage of thesubstrate due to thermal stress during the deposition steps, hence it issignificantly difficult to improve the throughput of the film depositionsystem. Also, the scaling-up of the substrate size inevitably requiresscaling-up of the film deposition system. An increased cost accompaniedby the increased volume in the vacuum system further increases theinitial investment, and as a result, it is difficult to achieve drasticcost reduction.

Although an increased yield is a valuable means for cost reduction, ayield near the limit has been achieved, and thus drastic cost reductionis difficult in view of the yield.

Patterning of each layer is performed by a photolithographic process.The photolithographic process essentially includes a coating step, anexposure step and a developing step of a resist film. After these steps,an etching step and a resist-removing step are required, hence the stepsfor patterning is a factor in increasing the number of steps for thinfilm deposition. This is a factor in the increased cost of thin filmdevice production.

Regarding the resist-coating step in the photolithographic process, onlyless than 1% of the resist solution dropped onto the substrate remainson the substrate as the resist film after spin coating, reducing theefficiency of the use of the resist solution.

Although a printing process has been proposed as a low cost processinstead of a large scale exposure system used in the exposure step, ithas not yet reached practical use due to problems such as processingaccuracy.

As described above, it is not possible to drastically reduce the cost ofthe TFT substrate, although the market requires drastic price reductionof the liquid crystal display devices.

It is an object of the present invention to provide a thin film deviceand a method for making the same, in which a part, or all of, the filmsin a thin film monolithic structure used for a liquid crystal displaydevice are deposited without a vacuum system in order to decreaseinitial investment and operation costs, increase the throughput andsignificantly decrease the production costs.

It is another object of the present invention to provide a thin filmdevice and a method for making the same, in which a thin film havingcharacteristics similar to those of a CVD or sputtered film is formed ofa coating film while achieving cost reduction.

It is a further object of the present invention to provide a thin filmdevice and a method for making the same, in which the consumption of acoating solution is decreased in the formation of the thin coating filmfor achieving cost reduction.

It is still another object of the present invention to provide a thinfilm device and a method for making the same, which is capable ofpatterning the formed film without a photolithographic process and,thus, reducing the cost.

It is a still further object of the present invention to provide a thinfilm device, a liquid crystal panel and an electronic device using thesame, in which a plane in contact with the liquid crystal can beplanarized by forming a pixel electrode with a coating film.

It is another object of the present invention to provide a thin filmdevice, a liquid crystal panel, and an electronic device using the same,in which a wiring layer can be used as a light-shielding layer for ablack matrix and the thin film device has a high aperture ratio.

It is still another object of the present invention to provide a liquidcrystal panel and an electronic device which enable cost reduction dueto use of an inexpensive thin film device.

DISCLOSURE OF INVENTION

According to an embodiment of the present invention, a thin film devicehas a thin film monolithic structure comprising a plurality of thinfilms including at least one insulating layer and at least oneconductive layer, wherein

at least one thin film in the thin film monolithic structure is formedof a coating film (excluding a spin-on-glass film having a basicstructure comprising siloxane bonds), which is obtained by applying asolution containing a constituent of the thin film followed byannealing.

A method for making the thin film device comprises the following stepsof:

applying a coating solution containing a constituent of the thin filmonto a substrate; and

forming a coating film (excluding a spin-on-glass film having a basicstructure comprising siloxane bonds) by annealing the coated surface ofthe substrate.

In the present invention, at least one layer in the thin film monolithicstructure is formed as a coating film without a vacuum system. As such acoating film, a spin-on-glass (SOG) film having a basic structurecomprising siloxane bonds, which has been used as a planarization layer,has been known. The organic SOG film is, however, readily etched duringan oxygen plasma process, whereas the inorganic SOG film readily crackseven if the film has a thickness of several thousand angstroms, hence itis rarely used solely as an interlevel insulating film, and is used asonly a planarization layer above a CVD insulating film.

In the present invention, an insulating layer and a conductive layercomposing a thin film monolithic structure are formed of a coating filmother than the SOG film, and the thin film can be planarized at the sametime. Because the coating film can be formed without a vacuum systemsuch as a CVD system or a sputtering system, a mass-production line canbe constructed with a significantly smaller investment compared toconventional systems, the throughput of the system can be increased, andthe cost of the thin film device can be drastically reduced.

The thin film monolithic structures include various structures, forexample, those including semiconductor layers, those including thin filmtransistors, and those including an underlying insulating layer and anupper protective insulating layer.

In these cases, it is preferable that all of the insulating layerscontained in the thin film monolithic structure be formed of a coatingfilm. A gate insulating layer requiring a critical film quality forensuring desired thin film transistor characteristics, however, may beformed by a method other than a coating process.

It is preferable that at least two thin films in the thin filmmonolithic structure be formed by a coating process in order to reducethe device cost which is a purpose of the present invention.

The insulating layer can be formed of a SiO₂ coating film, which isobtained by applying a solution containing a polymer having Si—N bonds(polysilazane), followed by a first annealing process in an oxygenatmosphere. Because the polysilazane having the above structure exhibitshigh cracking resistance and oxygen plasma resistance, a single layercan be used as an insulating layer having a given thickness.

It is preferable that the insulating layer be subjected to a secondannealing process at a temperature higher than that in the firstannealing process to further clean its surface. The second annealingprocess may be performed at a high temperature for a short period usinga laser or a lamp.

The semiconductor layer is formed by implanting an impurity into asilicon coating film, which is formed by applying a solution containingsilicon particles, followed by a first annealing process.

It is preferable that the semiconductor layer be subjected to a secondannealing process at a temperature higher than that in the firstannealing process to improve the crystallinity in the layer. The secondannealing process may also be performed at a high temperature for ashort period using a laser or a lamp.

Preferably, a method for diffusing an impurity into the silicon coatingfilm comprises the following steps of:

forming by coating an impurity-containing layer onto the silicon coatingfilm; and

diffusing the impurity into the silicon coating film by heating theimpurity-containing layer.

Conventionally, the high concentration impurity region which functionsas a source-drain region has been formed of an impurity-doped siliconfilm by a CVD system, or formed by introduction of an impurity by an ionimplanting process or an ion doping process. In the present invention, asource-drain region is formed by a step of applying and baking asolution to form a thin film containing an impurity, and by a step ofannealing the thin film at a high temperature for a short period using alamp or a laser to form a high concentration impurity region. The ionimplanting system and the ion doping system basically belong to vacuumsystems, and require extremely complicated mechanisms for generatingplasma, extracting ions, mass-separating the ions (for the ionimplanter), accelerating ions, collimating ions, scanning ions and soon. Hence these two systems have evidential high prices compared to thesystem for coating and annealing the thin film containing the impurity.

There are two methods for forming the conductive layer. In one method athin metal film is formed and in the other method a thin transparentconductive film is formed.

The formation of the thin metal film as a conductive layer includescoating of a solution containing conductive particles and thenevaporating the solvent by a first annealing process. A conductivecoating film can be thereby formed.

It is preferable that the conductive layer also be subjected to a secondannealing process at a temperature higher than that in the firstannealing process to reduce the resistance of the layer. The secondannealing process may be performed at a high temperature for a shortperiod using a laser or a lamp.

Preferably, a method for forming a transparent conductive film as aconductive layer comprises:

a first annealing step annealing the coated surface in an oxygen ornonreductive atmosphere; and

a second annealing step annealing the coated surface in a hydrogen orreductive atmosphere.

When forming the transparent electrode as the conductive layer, forexample, an organic acid containing indium and tin is used as a coatingsolution. Preferably in this case, a solvent used for adjusting theviscosity is evaporated (at, for example, a temperature of approximately100° C.) after coating, and then the above-mentioned first and secondannealing processes are performed. Indium oxide and tin oxide are formedduring the first annealing process, and the film is reduced during thesecond annealing process in a hydrogen or reductive atmosphere.

It is preferable that the temperature in the second annealing process belower than that in the first annealing process.

The transparent conductive coating film after the first annealingprocess can be prevented from thermal deterioration in the secondannealing process.

Preferably, the substrate is maintained in the nonoxidizing atmosphereafter the second annealing process until the substrate temperature isdecreased to 200° C. or less. The reoxidation of the transparentconductive coating film reduced during the second annealing process canbe thereby suppressed, and thus the sheet resistance of the transparentconductive coating film does not increase. It is preferable that thesubstrate be introduced into open air at a temperature of 100° C. orless in order to ensure prevention of the reoxidation. Because theresistivity of the coated ITO film decreases in proportion to the oxygendefects in the film, the reoxidation of the transparent conductivecoating film due to oxygen in the open air results in an increase in thespecific resistivity.

In the formation of the transparent conductive coating film, a coatingsolution containing indium (In) and tin (Sn) is applied onto thesubstrate. The coating film is oxidized in the first annealing processto form an ITO film. Using the coated ITO film, the conductive layer isalso usable for the transparent electrode.

When the surface of the ITO film is plated with a metal, the film can beused as a conductive layer other than the transparent electrode, and themetal plating can decrease the contact resistance.

It is preferable that a conductive sputtering film be formed on thecontact face of the coated ITO film by a sputtering process.

An example of the thin film monolithic structure is an active matrixsubstrate including pixel switching elements provided on theirrespective pixels, which are formed near intersections of a plurality ofdata lines with a plurality of scanning lines, and pixel electrodesconnected thereto.

A typical pixel switching element used in the active matrix substrate isa thin film transistor. The thin film transistor as the pixel switchingelement includes a gate electrode electrically connected to one of thescanning lines and a drain electrode electrically connected to one ofthe pixel electrodes.

It is preferable that the pixel electrodes be formed of a conductivecoating film in such a thin film monolithic structure. The surface inwhich the pixel electrodes are formed generally has steps, while thesurface of the conductive coating film is substantially planarized whenthe pixel electrode is formed of the conductive coating film. As aresult, rubbing can be satisfactorily performed and occurrence ofreverse-tilt domains can be prevented.

It is preferable that the conductive coating film used for the pixelelectrodes be a coated ITO film. The coated ITO film functions as atransparent electrode and is suitable for producing an active matrixsubstrate in a transmission liquid crystal display device.

The thin film transistor as the pixel switching element includes aninterlevel insulating film formed on the front surface of the gateelectrode, and the data line and pixel electrode are electricallyconnected to the source region and the drain region, respectively,through contact holes formed in the interlevel insulating film.

The interlevel insulating film may be composed of a lower interlevelinsulating film which lies at the lower side, and an upper interlevelinsulating film which is formed on the surface of the lower interlevelinsulating film. In this case, the data line is electrically connectedto the source region through a first contact hole formed in the lowerinterlevel insulating film. On the other hand, the pixel electrode iselectrically connected to the drain region through a second contact holeformed in the lower interlevel insulating film and the upper interlevelinsulating film.

In such a configuration, the data line and the pixel electrode areformed on different layers from each other, hence these do notshort-circuit each other even if they are formed at a position in whichthey overlap with each other. The periphery of the pixel electrode cantherefore be arranged above the data line and the scanning line.

As a result, no planar gap is present between the data line or scanningline and the pixel electrode. The data line and the scanning line cantherefore function as a black matrix having a light-shielding function.Accordingly, it is not required to form a light shielding layer as theblack matrix by an additional process.

Because the range capable of forming the pixel electrode is expanded,the aperture ratio of the pixel region is increased, resulting in abright display.

It is preferable that the pixel electrode formed of a conductive coatingfilm be electrically connected to the drain electrode through aconductive sputtering film.

Because the sputtering film has a lower contact resistance than that ofthe conductive coating film, the contact resistance can be reduced bypositioning the conductive sputtering film between the conductivecoating film and the source region.

It is preferable the conductive sputtering film be a sputtering ITO filmso as not to decrease the aperture ratio.

When the conductive coating film and the conductive sputtering film havethe same pattern, the accuracy in the patterning of the pixel electrodecan be improved, because a resist film can be formed on only theconductive coating film having high adhesiveness to the resist mask, andthe conductive coating film and the conductive sputtering film can besimultaneously patterned. Resist mask formation on the conductivesputtering film having low adhesiveness to the resist mask is notrequired, and a decrease in accuracy in the patterning can be avoided.

When the conductive coating film and the conductive sputtering film donot have the same pattern, it is preferable that the periphery of theconductive coating film lies outside of the periphery of the conductivesputtering film.

Resist masks are separately formed on the conductive coating film andthe conductive sputtering film and are separately subjected tosputtering by different steps. The accuracy of the patterning for theperiphery of the pixel electrode depends on the accuracy of thepatterning for the conductive coating film having a larger patterningdimension than that of the conductive sputtering film. The low accuracyof the patterning for the conductive sputtering film having lowadhesiveness to the resist mask does not affect the accuracy of thepatterning for the pixel electrode.

When the conductive sputtering film and the data line are present in thesame layer, these can be simultaneously formed of the same metalmaterial.

Alternatively, the conductive sputtering film may lie above the dataline. In this case, as these layers are formed by different steps, theselayers may be formed of the same material or different materials.

The interlevel insulating film may include a lower interlevel insulatingfilm at the lower side and an upper interlevel insulating film depositedon the surface of the lower interlevel insulating film, and the dataline and the conductive sputtering film may be formed on the surface ofthe upper interlevel insulating film. The data line is electricallyconnected to the source region through a first contact hole formed inthe lower interlevel insulating film. On the other hand, the conductivesputtering film is electrically connected to the drain region through asecond contact hole formed in the upper interlevel insulating film andthe lower interlevel insulating film. The conductive coating film isdeposited on the surface of the conductive sputtering film.

Alternatively, the data line and the conductive sputtering film may beformed in the same layer on the surface of the lower interlevelinsulating film. In this case, the data line is electrically connectedto the source region through a first contact hole formed in the lowerinterlevel insulating film. The conductive sputtering film iselectrically connected to the drain region through a second contact holeformed in the lower interlevel insulating film. Further, the conductivecoating film is deposited on the surface of the upper interlevelinsulating film, and electrically connected to the conductive sputteringfilm through a third contact hole formed in the upper interlevelinsulating film.

In accordance with another embodiment, a liquid crystal panel comprises:

an active matrix substrate provided with the above-mentioned thin filmdevice,

a counter substrate facing the active matrix substrate, and

a liquid crystal layer encapsulated between the active matrix substrateand the counter substrate.

In accordance with a further embodiment, an electronic device comprisesthe liquid crystal panel.

In these cases, the cost reduction in the thin film device enablesdrastic cost reduction of the liquid crystal panel and the electronicdevice using the liquid crystal panel.

In the above-mentioned solution coating step, it is preferable that thesolution be applied to only the coating region on the substrate to forma patterned coating film on the substrate, because a photolithographicprocess including many steps is not required. According to this process,consumption of the coating solution decreases and thus the operationcost can be reduced.

In accordance with still another embodiment of the present invention, amethod for making a thin film device is characterized in that apatterned coating film is formed on the substrate by:

preparing a coating solution dispenser head provided with a plurality ofliquid discharging nozzles, and

discharging the coating solution onto only the coating region on thesubstrate while relatively changing the positions of the substrate andthe liquid discharging nozzles.

This method can be achieved by, for example, an ink jet process. Becausethe coating solution is not wasted and no photolithographic process isrequired, this method greatly contributes to the investment costreduction and improved throughput. For example, in conventional coatingtechniques only approximately 1% of a dropped resist has been used as acoating film, whereas in the present invention 10% or more of a droppedresist can be used as a coating film. Of course, such a high coatingefficiency holds for the other coating films in the present invention,and thus the reduced use of the coating materials and the reduced timein the coating processes enable the cost reduction of liquid crystaldisplay devices.

It is preferable that these nozzles be independently controlled todischarge or not to discharge the coating solution, and positions of thesubstrate and the discharge nozzles be relatively changed whilecontrolling the coating timing on the nozzle. More precise patterncoating can thereby be achieved.

Such a coating process is applicable to coating of various coatingsolutions for forming coating films by other than coating of the resistfor forming a resist pattern. For example, if an insulating coating filmis pattern-coated, a contact hole can be formed simultaneously with thecoating.

As described above, in accordance with the present invention, a part orall of the thin films can be formed by applying and annealing asolution, hence a thin film device can be produced with an inexpensiveproduction unit having a high throughput.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram of a coating film deposition unit used in afirst embodiment in accordance with the present invention;

FIG. 2 is a block diagram of another coating film deposition unit usedin a first embodiment in accordance with the present invention;

FIG. 3 is a cross-sectional view of a coplanar-type TFT;

FIG. 4 is a cross-sectional view of a reverse stagger-type TFT;

FIG. 5 is a block diagram of an in-line-type coating film depositionunit used in a first embodiment in accordance with the presentinvention;

FIG. 6 is a block diagram of another in-line-type coating filmdeposition unit used in a first embodiment in accordance with thepresent invention;

FIG. 7 is a block diagram of a silicon-coating film deposition unit usedin a first embodiment in accordance with the present invention;

FIG. 8 is a block diagram of another silicon-coating film depositionunit used in a first embodiment in accordance with the presentinvention;

FIG. 9 is a flow chart illustrating a method for metal-plating onto anITO coating film surface;

FIG. 10 is a cross-sectional view of a production step of acoplanar-type TFT using an insulating layer containing an impurity inaccordance with the present invention;

FIG. 11 is a cross-sectional view of a production step of a reversestagger-type TFT using an insulating layer containing an impurity inaccordance with the present invention;

FIG. 12 is a block diagram of a solution coating unit used in a firstembodiment in accordance with the present invention;

FIG. 13 is an outlined schematic view illustrating a state of thesolution coating unit of FIG. 12 after spin coating;

FIG. 14 is a block diagram of another solution coating unit inaccordance with the present invention;

FIG. 15 is an enlarged partial view of the solution coating unit shownin FIG. 14;

FIG. 16 is an enlarged partial view of the solution coating unit shownin FIG. 14;

FIG. 17 is a schematic view of a TFT substrate forming a liquid crystaldisplay device;

FIG. 18 is an enlarged plan view of a portion of a pixel regionindependently formed on an active matrix substrate for a liquid crystaldisplay device in accordance with a second embodiment of the presentinvention;

FIG. 19 is a cross-sectional view taken along section I-I′ of FIG. 18;

FIG. 20 is a cross-sectional view illustrating a method for making theactive matrix substrate shown in FIG. 19;

FIG. 21 is a cross-sectional view illustrating the steps performed afterthe steps shown in FIG. 20;

FIG. 22 is an enlarged plan view of a portion of a pixel regionindependently formed on an active matrix substrate for a liquid crystaldisplay device in accordance with a third embodiment of the presentinvention;

FIG. 23 is a cross-sectional view taken along section II-II′ of FIG. 22;

FIG. 24 is a cross-sectional view illustrating the steps performed afterthe steps shown in FIG. 20 in the production of the active matrixsubstrate shown in FIG. 22;

FIGS. 25(A) and 25(B) are enlarged longitudinal cross-sectional viewsnear contact holes of a comparative example and an example in accordancewith the present invention, respectively;

FIG. 26 is a cross-sectional view of a structure in accordance with afourth embodiment of the present invention, taken along section II-II′of FIG. 22;

FIGS. 27(A) to 27(E) are cross-sectional views of a method for makingthe active matrix substrate shown in FIG. 26;

FIGS. 28(A) to 28(E) are cross-sectional views of the steps performedafter the steps shown in FIG. 27;

FIG. 29 is an enlarged plan view of a portion of a pixel regionindependently formed on an active matrix substrate for a liquid crystaldisplay device in accordance with a fifth embodiment of the presentinvention;

FIG. 30 is a cross-sectional view taken along section III-III′ of FIG.29;

FIGS. 31(A) to 31(F) are cross-sectional views illustrating the stepsperformed after the steps shown in FIG. 27 in the production of theactive matrix substrate shown in FIG. 29;

FIG. 32 is an enlarged plan view of a portion of a pixel regionindependently formed on an active matrix substrate for a liquid crystaldisplay device in accordance with a sixth embodiment of the presentinvention;

FIG. 33 is a cross-sectional view taken along section IV-IV′ of FIG. 32;

FIGS. 34(A) to 34(D) are cross-sectional views illustrating the stepsperformed after the steps shown in FIG. 27 in the production of theactive matrix substrate shown in FIG. 32;

FIG. 35 is an enlarged plan view of a portion of a pixel regionindependently formed on an active matrix substrate for a liquid crystaldisplay device in accordance with a seventh embodiment of the presentinvention;

FIG. 36 is a cross-sectional view taken along section V-V′ of FIG. 35;

FIGS. 37(A) to 37(C) are cross-sectional views illustrating the stepsperformed after the steps shown in FIG. 27 in the production of theactive matrix substrate shown in FIG. 35;

FIGS. 38(A) and 38(B) are schematic views of active matrix substratesfor liquid crystal display devices in accordance with anotherembodiment;

FIGS. 39(A) and 39(B) are enlarged longitudinal cross-sectional viewsnear contact holes of a comparative example and an example in accordancewith the present invention, respectively;

FIG. 40 is a block diagram of a liquid crystal display device includedin an electronic device in accordance with an eighth embodiment of thepresent invention;

FIG. 41 is an outlined cross-sectional view of a projector as an exampleof the electronic device using the liquid crystal display device of FIG.40;

FIG. 42 is a schematic view of a personal computer as another example ofthe electronic device;

FIG. 43 is an assembly view of a pager as a further example of theelectronic device; and

FIG. 44 is a schematic view of a liquid crystal display device providedwith a TCP.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will now be described in detail with reference tothe drawings.

FIRST EMBODIMENT

(Illustration of Thin Film Device Structure)

Two examples of thin film devices including TFTs are shown in FIGS. 3and 4.

FIG. 3 is a cross-sectional view of a TFT using a coplanar-typepolycrystalline silicon. An insulating underlayer 12 is formed on aglass substrate, and a polycrystalline silicon TFT is formed thereon. InFIG. 3, the polycrystalline silicon layer 14 comprises a source region14S and a drain region 14D which are highly doped with an impurity, anda channel region 14C therebetween.

A gate insulating film 16 is formed on the polycrystalline silicon layer14 and a gate electrode 18 and a gate line (not shown in the drawing)are formed thereon. A pixel electrode 22 composed of a transparentelectrode film is connected to the drain region 14D through an openingsection formed in an interlevel insulating film 20 and the gateinsulating film 16 thereunder, and a source line 24 is connected to thesource region 14S. A topmost protective film 26 may be omitted. Theinsulating underlayer 12 is provided for the purpose of prevention ofcontamination from the glass substrate 10 and of conditioning of thesurface for forming the polycrystalline silicon film 14, and may beomitted in some cases.

FIG. 4 is a cross-sectional view of a reverse stagger-type amorphoussilicon TFT. An insulating underlayer 32 is formed on a glass substrate30, and an amorphous silicon TFT is formed thereon. The insulatingunderlayer 32 is often omitted. In FIG. 4, a layer or a plurality oflayers of gate insulating films 36 are formed under a gate electrode 34and a gate line connected thereto. On the gate electrode 34, anamorphous silicon channel region 38C is formed, and a source region 38Sand a drain region 38D are formed by diffusing an impurity into theamorphous silicon. A pixel electrode 40 is electrically connected to thedrain region 38D through a metal lead layer 42, and a source line 44 iselectrically connected to the source region 38S. The metal lead layer 42and the source line are simultaneously formed.

A channel protective film 46 is formed on the channel region 38C toprotect the channel region 38C during etching of the source region 38Sand the drain region 38D, and may be omitted in some cases.

FIGS. 3 and 4 show basic TFT structures, and these structures may have avery wide range of modifications. For example, in order to increase theaperture ratio in the coplanar-type TFT in FIG. 3, a second interlevelinsulating film may be provided between the pixel electrode 22 and thesource line 24 to decrease the gap between the pixel electrode 22 andthe source line 24. Further, in order to decrease the wiring resistanceof the gate line not shown in the drawing and the source line 24 whichare connected to the gate electrode 18 and to increase the wiringlength, the gate line and the source line may be formed of multiplelayers. A light shielding layer may be formed on or under the TFTelement. In the reverse stagger-type TFT in FIG. 4, the wiring lines andthe insulating film may be formed of multiple layers for the purpose ofimprovement in the aperture ratio, a decrease in the wiring resistanceand a decrease in defects.

Most of these modifications to the basic structures in FIG. 3 or 4involve an increase in the number of thin layers deposited to form theTFT.

The following example shows a case in which various thin films in thethin film monolithic structures shown in FIGS. 3 and 4 are formed bycoating films which require no vacuum system.

(Method for Forming Insulating Coating Film)

FIG. 1 shows a coating film deposition unit which forms a thin film,e.g. an insulating film, by applying and annealing a solution. Thesolution which becomes the insulating film by annealing after coatingcontains a polysilazane (generic name for polymers having Si—N bonds). Atypical polysilazane is polyperhydrosilazane represented by[SiH₂NH]_(n), wherein n is an integer. The compound is commerciallyavailable under the commercial name “Tonen Polysilazane”, which ismanufactured by Tonen Corporation. If alkyl groups, e.g. methyl groupsor ethyl groups, are substituted for hydrogen atoms in [SiH₂NH]_(n), thecompound is called organic polysilazane to distinguish it from inorganicpolysilazane. In this embodiment, it is preferable that inorganicpolysilazanes be used.

After a polysilazane is mixed with a solvent such as xylene, thesolution is applied onto a substrate by spin coating. The coating filmis converted to SiO₂ by annealing in a steam- or oxygen-containingatmosphere.

A film for comparison is a spin-on-glass (SOG) film which is convertedto an insulating film by annealing after coating. The SOG film iscomposed of a polymer having siloxane bonds as a basic structure. TheSOG polymers include organic polymers having alkyl groups and inorganicpolymers not having alkyl groups, and alcohols and the like are used assolvents. The SOG film is used as an interlevel insulating film in anLSI for the purpose of planarization. The organic SOG film is readilyetched during an oxygen plasma process, whereas the inorganic SOG filmreadily forms cracks even if it has a thickness of several hundredangstroms, hence these films are not used as a single layer ofinsulating film, but are used as a planarization layer on a CVDinsulating film.

In contrast, polysilazane has high crack resistance and oxygen plasmaresistance, and can be used as a single layer of insulating film havingan appropriate thickness. A case using polysilazane will now bedescribed.

In the present invention, at least one layer, and preferably a pluralityof layers, in the thin film monolithic structure are formed of coatingfilms other than the SOG film which has siloxane bonds as a basicstructure. Additional SOG films can be used within the range satisfyingthe above condition.

In FIG. 1, a loader 101 separately removes a plurality of substratesstored in a cassette and moves the glass substrates onto a spin coater102. In the spin coater 102, as shown in FIG. 12, a substrate 132 isfixed by vacuum on a stage 130, and then a polysilazane solution 138 isdropped onto the substrate 132 through a nozzle 136 of a dispenser 134.A mixed solution of polysilazane and xylene is stored in a containercalled a canister at a solution storage section 105 shown in FIGS. 1 and12. The mixed solution of polysilazane and xylene is supplied to thedispenser 134 from the solution storage section 105 through a feedingpipe 140 and is coated onto the substrate. Then, as shown in FIG. 13,the polysilazane solution 138 is dispersed onto the entire surface ofthe glass substrate 132 by the rotation of the stage 130. Most of xyleneis evaporated in this process. A control section 106 shown in FIG. 1controls the speed and time of rotation of the stage 130 to increase thespeed to 1,000 rpm in several seconds, to maintain 1,000 rpm forapproximately 20 seconds, and to stop the rotation after severalseconds. In such a coating condition, the polysilazane coating film hasa thickness of approximately 7,000 angstroms. Next, the glass substrateis transferred to an annealing section 103 and annealed at a temperatureof 100 to 350° C. for 10 to 60 minutes in a steam atmosphere to modifythe polysilazane to SiO₂. A temperature control section 107 controls theannealing step. The length of the annealing section 103 and the capacityfor holding the substrates in the annealing section 103 is determined soas to match the tact? time of the spin coater 102 with the annealingtime in order to enhance the performance of the coating-type insulatingfilm deposition unit. Because the polysilazane solution contains, forexample, xylene, and because hydrogen and ammonia form during themodification, at least the spin coater 102 and the annealing section 103require a ventilating system 108. The glass substrate provided with theinsulating film formed during the annealing process is stored into acassette by an unloader 104.

The coating-type insulating film deposition unit of the presentinvention shown in FIG. 1 has a significantly simplified systemconfiguration compared to conventional CVD systems, and thus the priceof the unit is remarkably decreased. Further, the unit has a higherthroughput than the CVD systems, decreased maintenance, and a high networking rate. These advantages enables drastic cost reduction of liquidcrystal display devices.

The coating-type insulating film deposition unit shown in FIG. 1 canform all the insulating films shown in FIG. 3; that is, the insulatingunderlayer 12, the gate insulating layer 16, the interlevel insulatingfilm 20 and the protective film 26. When an additional insulating layeris formed between the pixel electrode 22 and the source electrode 24,the formation of the coating film using the unit shown in FIG. 1 isparticularly effective for planarization of the surface of theadditional insulating layer. The insulating underlayer 12 and theprotective film 26 may be omitted in some cases.

Because the gate insulating film 16 is an important insulating filmdetermining electrical characteristics of the TFT, interfacialcharacteristics between the film and the silicon film, as well as thefilm thickness and the film quality, must be controlled.

In order to achieve such control, it is preferred to clean the surfaceof the silicon film 14 before forming the gate insulating film 16 bycoating, and to use a coating-type insulating film deposition unit shownin FIG. 2. The unit shown in FIG. 2 is provided with a first annealingsection 103A having the same function as the annealing section of theunit shown in FIG. 1, and a second annealing section 103B in front of anunloader 104. After the annealing in the first annealing section 103A,the second annealing section 103B preferably performs an annealingprocess at a temperature of 400 to 500° C., which is higher than theannealing temperature of the first annealing section 103A, for 30 to 60minutes, or an annealing process at a high temperature for a shortperiod, such as by lamp annealing or laser annealing.

As a result, the insulating films such as the gate insulating film 16are further densified and have improved film quality and interfacialcharacteristics as compared to the annealing only in the annealingsection shown in FIG. 1.

Regarding the interfacial characteristics, a CVD film formed in a vacuumatmosphere can be easily controlled compared to the insulating coatingfilm. When a high performance TFT is required, therefore, the gateinsulating film may be formed of a CVD film and the other insulatingfilms in the TFT may be formed of insulating coating films in accordancewith the present invention.

In the TFT structure in FIG. 4, the insulating underlayer 32, the gateinsulating film 36 and the channel protective film 46 can use theinsulating coating film of the present invention.

(Method for Forming Silicon Coating Film)

Using a coating solution containing silicon particles, which is storedin the solution storage section 105 shown in FIG. 1 or 2, a siliconcoating film can be formed using the same unit shown in FIG. 1 or 2.

The size of the silicon particles contained in the coating solutionranges, for example, from 0.01 to 10 μm. The size of the siliconparticles is determined by the thickness of the silicon coating film. Inthe silicon particles obtained by the present inventors, particles ofapproximately 1 μm occupy 10%, and those of 10 μm or less occupy 95%.The silicon particles having such a size distribution are furtherpulverized with a pulverizer to obtain silicon particles having adesired size distribution.

The silicon particles having a given size distribution are stored in thesolution storage section 105 as a suspension in a solvent such asalcohol. The suspension composed of the silicon particles and alcohol isdischarged onto a substrate transferred onto the spin coater 106 fromthe loader 105. The stage 130 is rotated under the same coatingcondition as in the insulating coating film to disperse the coating filmof the silicon particles on the substrate, wherein most of alcohol isevaporated.

Next, the substrate is annealed in the annealing section 103 or thefirst annealing section 103A under the same annealing condition as inthe insulating coating film. The silicon particles react with each otherto form a crystallized silicon film on the substrate.

In the case using the unit in FIG. 2, the substrate is further annealedin the second annealing section 103B at a higher temperature than thatin the first annealing section 103A. It is preferable that the annealingbe performed in a short time by laser annealing or lamp annealing.

Reannealing in the second annealing section 103B improves crystallinityand density in the silicon film and adhesion to other films, as comparedto the annealing only in the first annealing section 103A.

FIGS. 5 and 6 are block diagrams of film deposition units forcontinuously forming a silicon coating film and an insulating coatingfilm.

In the film deposition unit in FIG. 5, a loader 101, a first spin coater102A, a first annealing section 103A, a second annealing section 103B, asecond spin coater 102B, an annealing section 103 and an unloader 104are in-line-connected. The first spin coater 102A is connected with afirst solution storage section 105A storing a suspension of siliconparticles and alcohol and a first control section 106A. The second spincoater 102B is connected with a second solution storage section 105Bstoring a mixed solution of polysilazane and xylene and a second controlsection 106B.

When using the unit in FIG. 5, the number of loading and unloading stepseach decreases once and the throughput is further improved.

The film deposition unit in FIG. 6 is a modification of the filmdeposition unit in FIG. 5, in which the second annealing section 103B isplaced after the annealing section 103 for the insulating coating film.In this case, the silicon film provided with an insulating cap layer iscrystallized in the second annealing section 103B by laser annealing orthe like. Because the insulating layer decreases reflectance of thesilicon surface, the laser energy is effectively absorbed in the siliconfilm. Further, the silicon film has a smooth surface after the laserannealing.

The annealing section 103 and the second annealing section 103B in FIG.6 may be unified into a common annealing section. In this case, thecommon annealing section can simultaneously perform firing of theinsulating coating film and annealing for crystallization of the siliconfilm thereon.

(Another Method for Forming Silicon Coating Film)

FIG. 7 shows a coating-type silicon film deposition unit in which asilicon film is formed by coating and annealing of a coating solution.Monosilane (SiH₄) and disilane (Si₂H₆) are used for forming a siliconfilm in a CVD process, whereas higher silanes such as disilane andtrisilane (Si₃H₈) are used in the present invention. Boiling points ofsilanes are −111.9° C. for monosilane, −14.5° C. for disilane, 52.9° C.for trisilane, and 108.1° C. for tetrasilane (Si₄H₁₀), respectively.Monosilane and disilane are therefore gaseous at room temperature andpressure, whereas higher silanes such as trisilane are liquid. Asdisilane is liquified at minus several tens ° C., it can be used as acoating film. Hereinafter, a case using trisilane will be primarilydescribed.

In FIG. 7, after glass substrates are separately taken out by a loader201 from a cassette and transferred into a load lock chamber 202, theload lock chamber 202 is evacuated by a ventilating system 711. Afterevacuating at a given pressure, the glass substrate is transferred ontoa spin coater 203 which is also evacuated at a similar pressure, andtrisilane in a trisilane storage section 207 is applied onto the glasssubstrate through a dispenser. The spin coater 203 rotates at a rate of100 to 2,000 rpm for several seconds to 20 seconds to spin-coattrisilane. The glass substrate after spin-coating trisilane isimmediately transferred to a first annealing section 204 having asimilar reduced pressure as above, and annealed at 300 to 450° C. forseveral tens of minutes to form a silicon film with a thickness ofseveral hundred angstroms. Then, the glass substrate is transferred to asecond annealing section 205 having a similar reduced pressure as above,and annealed at a high temperature for a short time by laser or lampannealing. The silicon film is thereby crystallized. After this, theglass substrate is transferred to a load lock chamber 206, and istransferred to an unloader 207 to a cassette after the load lock chamber206 is released to atmospheric pressure with gaseous nitrogen.

Preferably, two ventilating systems 211 are provided, that is, oneconnected to the two load lock chambers 202 and 206 and the otherconnected to the spin coater 203 and the first and second annealingsections 204 and 205. The spin coater 203, the first annealing section204 and the second annealing section 205 are always evacuated by theventilating system 211 to maintain a reduced pressure (near 1.0 to 0.5atmospheres) of an inert atmosphere, in order to prevent leakage ofgaseous toxic silanes. The threshold limit value (TLV) of monosilane is5 ppm, and it is considered that higher silanes such as disilane havesimilar TLVs. Silanes spontaneously burn at room temperature in air andexplosively burn at high temperatures. Thus, at least the ventilatingsystem 211 connected to the spin coater 203 and to the first and secondannealing sections 204 and 205 is connected to an exhaust gas disposalunit 212 which makes silanes non-toxic. The processing chambers 201 to207 in FIG. 7 are coupled with each other with gate valves which openand close when the glass substrate is transferred so that gaseoussilanes do not flow into the two load lock chambers.

The main section of the spin coater 203 is substantially the same as inFIG. 12, and in FIG. 7. Preferably the temperature at the stage, onwhich the glass substrate is fixed by vacuum, is controlled by atemperature controlling section 210. The temperature is controlled toroom temperature and preferably approximately 0° C. when usingtrisilane, or at −40° C. or less and preferably −60° C. or less whenusing disilane. It is preferable that the solution storage section 208for disilane or trisilane and a feed line (not shown in the drawing) becontrolled to a temperature similar to the stage temperature by thetemperature control section 210.

Disilane or trisilane must be applied as a liquid at a temperature lowerthan its boiling point. Because trisilane has a vapor pressure ofapproximately 0.4 atm at room temperature and pressure and disilane hasa vapor pressure of approximately 0.3 atm at −40° C. and ordinarypressure, it is preferable that the temperature of the silane andsubstrate be decreased as much as possible in order to reduce the vaporpressure as much as possible.

The spin coater 203 and the first and second annealing sections 204 and205 may be pressurized with an inert gas in order to further reduce thevapor pressure of disilane or trisilane and improve the uniformity ofthe coating film. As the boiling temperature of disilane or the likeincreases in the pressurized state and the vapor pressure decreases at agiven temperature, the spin coater 203 can be set at a temperaturehigher than the above-mentioned temperature and near the roomtemperature. In this case, it is preferable that each chamber has adouble layer structure in view of leakage of trisilane or the like, inwhich an outer structure is provided out of the pressurized structureand leaked silane or the like in the outer structure is evacuatedthrough another ventilating system. The exhaust gas is disposed in theexhaust gas disposal unit 212.

Also, silane gas remaining in the spin coater 203 and the first andsecond annealing section 204 and 205 is evacuated by the ventilatingsystem 211.

In FIG. 8, the silicon film deposition unit shown in FIG. 7 and theinsulating film deposition unit shown in FIG. 1 are in-line-connected toeach other. In other words, the spin coating section 102 and theannealing section 103 shown in FIG. 1 are introduced between the secondannealing section 205 and the load lock chamber 206 in FIG. 7.

In FIG. 8, the steps for crystallizing the silicon film in the secondannealing section 205 by laser annealing are the same as the steps inthe unit shown in FIG. 7. The crystallized silicon film is transferredonto the spin coater 102 to apply a polysilazane or inorganic SOG film.The coating film is modified into an insulating film in the annealingsection 103.

The spin coater 203 and the first and second annealing sections 204 and205 are under reduced pressure of an inert gas atmosphere as in FIG. 7.The spin coater 102 for the insulating film and the annealing section103 are under ordinary pressure in FIG. 1, whereas those in FIG. 8 areunder reduced pressure of an inert gas atmosphere. These chambers areevacuated by the ventilating system 108.

The silicon film formed by the unit shown in FIG. 8 is not exposed toopen air, because the insulating film is formed on the silicon film inthe inert atmosphere. The interface between the silicon film and theinsulating film is therefore controlled to determine characteristics ofthe TFT element, resulting in improvement in the characteristics of theTFT element and uniformity of these characteristics.

In FIG. 8 the insulating film on the silicon film is formed aftercrystallization of the silicon film. However, the insulating film may beformed after the first annealing step of the silicon film and thesilicon film may be crystallized after annealing of the insulating film.Also, in this case, the silicon film provided with the insulating caplayer is crystallized by laser annealing as in FIG. 6. Because theinsulating film decreases the reflectance of the silicon surface, laserenergy is effectively absorbed in the silicon film. The silicon film hasa smooth surface after the laser annealing.

(Method for Diffusing Impurity into Silicon Coating Film)

Although an impurity may be diffused into a silicon film using aconventional ion implanting system, it is preferable that an insulatinglayer containing an impurity be applied onto the silicon layer and thenthe impurity be diffused into the underlying silicon film.

The insulating layer containing the impurity may be formed by the unitshown in FIG. 2. In this embodiment, an SOG film containing phosphorusglass or boron glass is applied as a coating film containing animpurity. When forming an n-type high-impurity region, the SOG film as acoating film containing an impurity is formed using a solution composedof a siloxane polymer and an ethanol or ethyl acetate solvent (Sicontent: several wt %), and containing several hundred μg of P₂O₅ per100 ml of solution.

In this case, the coating solution is stored in the solution storagesection 105 in FIG. 2 and applied onto the substrate by the spin coater102. The substrate on the spin coater 102 is rotated at several thousandrpm to obtain an SOG film with a thickness of several thousandangstroms. The coating film containing the impurity is annealed at 300to 500° C. in the first annealing section 103A to form a phosphorusglass film containing several mol percent of P₂O₅. The TFT substrateprovided with the phosphorus glass film is annealed in the secondannealing section 103 at a high temperature for a short time by laserannealing, such that the impurity in the SOG film is diffused into theunderlying silicon film and a high impurity region is formed in thesilicon film. The TFT substrate is stored into a cassette by theunloader 104.

In the formation of the source and drain regions, both the coating stepand the annealing step at a high temperature for a short time can becompleted within one minute, resulting in high productivity. Althoughthe annealing step requires several tens of minutes, the tact time canbe reduced by optimizing the length and structure of the annealing oven.

FIGS. 10 and 11 are cross-sectional views of TFTs provided with thecoating film containing the impurity. FIG. 10 shows a coplanar-type TFTcorresponding to that in FIG. 3, in which an insulating underlayer 12 isformed on a glass substrate 14, and a silicon layer 14 is pattern-formedthereon. A gate insulating film 16 is removed by etching using a gateelectrode 18 as a mask, a silicon layer is temporally exposed in regionswhich will be a source and a drain. The coating film 50 containing theimpurity is formed so as to come into contact with the source and drainregions 14S and 14D in the silicon film. Phosphorus contained in thecoating film 50 is diffused into the silicon film by thehigh-temperature, short-time annealing step and n-type source and drainregions 14S and 14D having sheet resistances of 1 KΩ/□ are formed.

As shown in the cross-sectional view of the TFT shown FIG. 3, thefollowing steps include forming an interlevel insulating film, providinga contact hole, forming a pixel electrode and forming source wiring. Inthe formation of the interlevel insulating film, the interlevelinsulating film may be formed of a coating film after the coating film50 containing the impurity is removed, or the interlevel insulating filmmay be formed on the coating film 50 containing the impurity. As themethod for forming the interlevel insulating film on the coating film 50containing the impurity forms two insulating layers, the occurrence ofshort-circuits between the source line and the gate line in the liquidcrystal display device is decreased.

FIG. 11 shows a reverse stagger-type TFT corresponding to that in FIG.4, in which an insulating underlayer 32 is formed on a glass substrate30, and a gate electrode 35 is formed thereon. A silicon layer 33 ispattern-formed through a gate insulating film. An insulating film 52functions as a protective film in the channel region and also as a maskto impurity diffusion, and is formed of an insulating coating film.

An insulating film 54 containing an impurity is formed as an insulatingcoating film in contact with the insulating film 52 as the mask andregions of the silicon film 33 which will be a source region 33S and adrain region 33D. When the insulating film 54 containing the impurity isannealed at a high temperature for a short time, phosphorus contained inthe insulating film is diffused into the silicon film 33 and n-typesource and drain regions 33S and 33D having sheet resistances ofapproximately 1 KΩ/□ are formed.

As shown in the cross-sectional view of the TFT shown FIG. 4, after theinsulating film 54 containing the impurity is removed, a pixelelectrode, source wiring, a drain electrode and connecting sections areformed in that order.

In accordance with the present invention, the source and drain regionsin the coplanar-type TFT are formed by forming a coating film and thesucceeding high-temperature, short-time annealing instead of aconventional ion implanting or an ion doping. Hence a TFT can be madeusing an inexpensive unit having a high throughput. In the reversestagger-type TFT shown in FIG. 4, the source and drain regions areformed by the high-temperature, short-time annealing step instead of theCVD process. Hence a liquid crystal display device can be made using aninexpensive unit having a high throughput as in the coplanar-type TFT.

(Method for Forming Conductive Coating Film)

A method for forming a conductive coating film by applying a solutioncontaining conductive particles will now be described. The conductivecoating film is also made using the unit shown in FIG. 1 or FIG. 2. Theliquid stored in the solution storage section 105 in FIG. 1 or FIG. 2 isa suspension of conductive fine particles composed of metal or the likein, for example, an organic solvent. For example, a dispersion of silverparticles with a size of 80 to 100 angstroms in an organic solvent, suchas terpineol or toluene, is discharged onto the substrate through thespin coater 102. The substrate is rotated at 1,000 rpm to spin-coat thecoating solution on the substrate. The substrate is annealed at 250 to300° C. in the annealing section in FIG. 1 or the first annealingsection in FIG. 2 to form a conductive film with a thickness of severalthousand angstroms. Examples of conductive materials include Au, Al, Ni,Co, Cr and ITO, and a conductive film can be formed of particles ofthese materials using the conductive coating film deposition unit.

Because the resulting conductive film is an aggregate of fine particlesand is very active, the spin coater 102, the annealing section or thefirst annealing section 103A must be in an inert gas atmosphere.

The resistance of the conductive coating film will be greater by oneorder of magnitude than the bulk resistance. In this case, theconductive coating film may be further annealed at 300 to 500° C. in thesecond annealing section 103B shown in FIG. 2 to decrease the resistanceof the conductive film. At the same time, the contact resistance of thesource region of the TFT with the source line formed of the conductivecoating film, and the contact resistance of the drain region with thepixel electrode formed of the conductive coating film, can be decreased.Introduction of a high-temperature, short-time annealing step by lamp orlaser annealing will further decrease the resistance of the conductivecoating film and the contact resistances. Further, a plurality of layerscomprising different metals may be formed in order to improvereliability. Since Ag is relatively easily oxidized in air, theformation of an Al or Cu layer, which is slightly oxidized in air, onthe Ag layer is preferable.

(Method for Forming Transparent Electrode)

A method for a transparent electrode using an ITO coating film will nowbe described. The ITO coating film may also be formed using the unitshown in FIG. 2. The coating solution used in this embodiment contains8% of a mixture of an organic indium and an organic tin in a ratio of97:3 in xylene (for example, manufactured by Asahi Denka Kogyo K.K.,trade name: ADEKA ITO coating film/ITO-130L). The ratio of the organicindium to the organic tin in the coating solution may be in a range from99:1 to 90:10. The coating solution is stored in the solution storagesection 105 in FIG. 2.

The coating solution is discharged onto the substrate by the spin coater102 and spin-coated by the rotation of the substrate.

The annealing conditions of the coating film were as follows. First, thesubstrate was annealed in an air or oxygen atmosphere at 250° C. to 450°C. for 30 minutes to 60 minutes in the first annealing section shown inFIG. 2. Next, it was annealed in a hydrogen-containing atmosphere at200° C. to 400° C. for 30 minutes to 60 minutes in the second annealingsection 103B. As a result, organic components are removed and a mixedfilm (ITO film) composed of indium oxide and tin oxide is formed. Afterthe above-mentioned annealing steps, the ITO film with a thickness ofapproximately 500 angstroms to 2,000 angstroms has a sheet resistance of10² Ω per sheet to 10⁴ Ω per sheet and a light transmittance of 90% ormore, and exhibits satisfactory characteristics as the pixel electrode.Although the sheet resistance of the ITO film after the first annealingstep is of the order of 10⁵ Ω per sheet to 10⁶ Ω per sheet, the sheetresistance after the second annealing step decreases to the order of 10²Ω per sheet to 10⁴ Ω per sheet.

Regarding the formation of the ITO coating film, the ITO film and theinsulating coating film can be formed by an in-line process using theunit shown in FIG. 5 or FIG. 6. The active ITO film surface cantherefore be immediately protected with the insulating film.

(Method for Forming Conductive Layer)

This method includes the formation of a metal plating layer on the ITOcoating film.

FIG. 9 is a flow chart of Ni plating on the ITO coating film. In Step 1of FIG. 9, the ITO film is formed by the above-mentioned method. In Step2, the surface of the ITO coating film is slightly etched to activatethe surface. In Step 3, as a pretreatment for Ni plating in Step 4, aPd/Sn complex is adhered onto the surface of the ITO coating film andthen Pd is precipitated on the surface.

In the Ni plating of Step 4, Pd precipitated on the ITO coating film isreplaced with Ni to form a Ni plating layer by, for example, anelectroless plating process. The Ni plating layer becomes more dense byannealing in Step 4.

Finally, in Step 5, a noble metal plating layer, for example, an Auplating layer, as an antioxidant layer is formed on the Ni plating layerto form a conductive layer.

Conductive layers other than the transparent electrode can be formedfrom the ITO coating film base by forming plating layers.

(Coating Method other than Spin Coating)

FIGS. 14 to 16 show a coating unit which applies a solution forming athin film or a resist solution used as a mask in photoresist etching. Inthis embodiment, a resist is exemplified as the solution to be coated.The coating unit can be also applied to the formation of various coatingfilms other than the resist coating.

In FIG. 14, a substrate 302 is fixed by vacuum on a stage 301. Theresist is supplied to a dispenser head 304 through a feeding pipe 306from a solution storage section 307. The resist is applied onto thesubstrate 302 as numerous dots 303 from a plurality of nozzles 305provided on the dispenser head 307.

FIG. 15 is a detailed cross-sectional view of the nozzle 305. The nozzlestructure in FIG. 15 is similar to that of an ink jet printer, and theresist is discharged by vibration of a piezoelectric element. The resistreaches a cavity section 313 through an inlet section 311 and a supplyport 312. A vibration plate 315 moves in cooperation with vibration of apiezoelectric element 314 in close contact with the vibration plate 315and the volume in the cavity 313 decreases or increases. When the volumein the cavity 313 decreases, the resist is discharged from the nozzle316, and when the volume in the cavity 313 increases the resist issupplied to the cavity 313 from the supply port 312. As shown in FIG.16, for example, a plurality of nozzles 316 are two-dimensionallyarranged, the resist is applied onto the entire substrate as dots byrelative movement of the substrate 302 or the dispenser 304, as shown inFIG. 14.

In FIG. 16, the array pitches of the nozzles 316 are several hundred μmfor the lateral pitch P1 and several mm for the longitudinal pitch P2.The nozzle 316 has a bore of several tens of μm to several hundred μm.The volume of the resist discharged in a cycle ranges from several tensof ng to several hundred ng, and the diameter of the discharged dropletsranges from several tens of μm to several hundred μm.

The applied resist dot has a circular shape of several hundred μmimmediately after it is discharged from the nozzle 305. When applyingthe resist onto the entire substrate, the pitch of the dots 303 is setto several hundred μm and the substrate is rotated at several hundred toseveral thousand rpm for several seconds to form a coating film having auniform thickness. The thickness of the coating film can be controlledby the bore of the nozzle 316 and the pitch of the dots 303, as well asthe rotation rate and time of the substrate.

The resist coating process is an ink jet-type liquid coating process andthe resist is applied onto the entire substrate as dots. Because thesubstrate is moved or rotated so as to apply the resist to nonresistportions between dots 303, the resist is effectively used. This processis also applicable to the formation of the insulating film, silicon filmand conductive film instead of the coating process, and thus greatlycontributes to cost reductions of liquid crystal display devices.

As the bore of the nozzle 316 can be further decreased in the inkjet-type liquid coating, the solution can be applied to form a linearpattern with a width of 10 to 20 μm. Use of this process in theformation of the silicon film or a conductive film permits directpatterning which requires no photolithographic process. When the designrequirement of the TFT is several tens of μm, a combination of thedirect patterning with a coating-type thin film deposition processpermits producing liquid crystal display devices without a CVD system, asputtering system, an ion implanting system, an ion doping system, anexposure system and an etching system. In other words, liquid crystaldisplay devices can be produced by an ink jet-type liquid coating unitin accordance with the present invention and an annealing unit such as alaser or lamp annealing unit.

In the first embodiment, although a TFT active matrix substrate isexemplified as a thin film device, the technologies in the firstembodiment are also applicable to other active matrix substrates,two-terminal and three-terminal elements as pixel switching elementscomposed of MIM (metal-insulator-metal) or MIS(metal-insulator-silicon). For example, the thin film monolithicstructure of an MIM active matrix substrate includes no semiconductorlayer, and consists of a conductive layer and an insulating layer, andthe present invention is also applicable to such a case. Further, thepresent invention is applicable to various display devices other thanactive matrix substrates, for example, an electro-luminescence device.In addition, the present invention is applicable to thin film deviceshaving various thin film monolithic structures comprising a conductivelayer, an insulating layer and a semiconductor layer, such assemiconductor devices including TFTs and DMDs (digital mirror devices).

Second to Seventh Embodiments will now be described in which the presentinvention is applied to active matrix substrates for liquid crystaldisplay devices and, in particular, pixel electrodes are formed byconductive coating films.

SECOND EMBODIMENT

FIG. 18 is an enlarged partial plan view of pixel regions formed on anactive matrix substrate for a liquid crystal display device, and FIG. 19is a cross-sectional view taken along section I-I′ of FIG. 18.

In FIGS. 18 and 19, the active matrix substrate 400 for the liquidcrystal display device is divided into a plurality of pixel regions 402by data lines Sn, Sn+1. . . and scanning lines Gm, Gm+1. . . on aninsulating substrate 410, and each of the pixel regions 402 is providedwith a TFT 404. The TFT 404 is provided with a channel region 417forming a channel between a source region 414 and a drain region 416, agate electrode 415 opposing to the channel region 417 with a gateinsulating film 413 formed therebetween, an interlevel insulating film421 formed on the top face of the gate electrode 415, a source electrode431 electrically connected to the source region 414 through a contacthole 421A formed in the interlevel insulating film 421, and a pixelelectrode 441 composed of an ITO film which is electrically connected tothe drain electrode 416 through a contact hole 421B formed in theinterlevel insulating film 421. The source electrode 431 is a part ofthe data lines Sn, Sn+1. . . , and the gate electrode 415 is a part ofthe scanning lines Gm, Gm+1 . . . .

The pixel electrode 441, as well as the source electrode (data line)431, is formed on the interlevel insulating film 421. The pixelelectrode 441 is therefore formed such that the peripheries 441A and441B parallel to the data lines Sn and Sn+1 lie at positionsconsiderably inside the data lines Sn and Sn+1 to prevent the occurrenceof short-circuits between these electrodes.

FIGS. 20(A) to 20(D) and FIGS. 21(A) to 21(C) are cross-sectional viewsillustrating manufacturing steps of the active matrix substrate in thisembodiment.

In the production of such an active matrix substrate 400, first ageneral-purpose nonalkaline glass is prepared as the insulatingsubstrate 410, as shown in FIG. 20(A). After the insulating substrate410 is cleaned, a protective underlayer 411 composed of a silicon oxidefilm is formed on the insulating substrate 410 by a chemical vapordeposition (CVD) process or a physical vapor deposition (PVD) process.Examples of CVD processes include a low pressure CVD (LPCVD) process anda plasma enhanced CVD (PECVD) process. A typical PVD process is asputtering process. The protective underlayer 11 may be omitted in viewof impurities contained in the insulating substrate 410 and cleanlinesson the substrate surface.

Next, an intrinsic semiconductor film 406, such as a silicon film, whichshould be an active layer of the TFT 404, is formed. The semiconductorlayer can be also formed by a CVD or PVD process. The resultingsemiconductor film 406 can be used as an amorphous silicon semiconductorlayer, such as a channel region of the TFT. Alternatively, as shown inFIG. 20(B), the semiconductor film 120 may be irradiated with opticalenergy such as laser light, or electromagnetic energy, to promotecrystallization.

After a resist mask having a given pattern is formed, the semiconductorfilm 406 is patterned using the resist mask to form insularsemiconductor films 412, as shown in FIG. 20(C). After forming thesemiconductor films 412, a gate insulating film 413 is formed by a PVDor CVD process.

A thin film as a gate electrode composed of an aluminum film or the likeis formed by a sputtering process. In general, the gate electrode andgate lead are formed of a common metal material by the same process.After depositing the gate electrode thin film, as shown in FIG. 20(D),gate electrodes 415 are formed by patterning. Scanning lines are alsoformed in this step. Impurity ions are introduced into eachsemiconductor film to form a source region 414 and a drain region 416. Asection not doped with impurity ions functions as a channel region 417.As the gate electrode 415 functions as a mask of ion implanting in thismethod, the TFT has a self-alignment structure in which the channelregion 417 is formed only under the gate electrode 415; however, the TFTmay be an offset gate structure or an LDD structure. Impurity ions maybe introduced by an ion doping process which implants hydride of theimpurity element and hydrogen using a mass-nonseparation-type ionimplanting system, or by an ion implanting system which implants onlypredetermined impurity ions using a mass-separation-type ion implantingsystem. Examples of material gases used in the ion doping processinclude hydrides of implanted impurities, such as phosphine (PH₃) anddiborane (B₂H₆) which are diluted in hydrogen to a concentration ofapproximately 0.1%.

Next, as shown in FIG. 21(A), an interlevel insulating film 421 composedof a silicon oxide film is formed by a CVD or PVD process. After ionimplantation and forming the interlevel insulating film 421, theinterlevel insulating film 421 is annealed at a temperature of 350° C.or less for several tens of minutes to several hours in a given thermalenvironment to activate the implanted ions and to bake the interlevelinsulating film 421.

Next, as shown in FIG. 21(B), contact holes 421A and 421B are formed atpositions of the interlevel insulating film 421 corresponding to thesource region 414 and the drain region 416. An aluminum film or the likeis formed by a sputtering process, and patterned to form a sourceelectrode 431. A data line is also formed in this step.

Next, as shown in FIG. 21(C), an ITO film 408 is formed on the entireinterlevel insulating film 421 by a coating process.

Various liquid or paste coating materials can be used in the coatingprocess. Among these coating materials, liquid materials are applicableto a dipping or spin coating process, paste materials are applicable toa screen printing process. The coating material used in the SecondEmbodiment contains 8% of a mixture of an organic indium and an organictin in a ratio of 97:3 in xylene (for example, manufactured by AsahiDenka Kogyo K.K., trade name: ADEKA ITO coating film/ITO-130L), as inthe First Embodiment, and is spin-coated on the top face of theinsulating substrate 410 (on the interlevel insulating film 20). Theratio of the organic indium to the organic tin in the coating materialmay be in a range from 99:1 to 90:10.

In the Second Embodiment, the film coated on the insulating substrate410 is annealed (baked) after removing the solvent and drying it. Afterthe film is annealed in an air or oxygen atmosphere at 250° C. to 450°C. for 30 minutes to 60 minutes, it is reannealed in a hydrogenatmosphere at 200° C. to 400° C. for 30 minutes to 60 minutes. As aresult, organic components are removed and a mixed film (ITO film) ofindium oxide and tin oxide is formed. After the above-mentionedannealing steps, the ITO film with a thickness of approximately 500angstroms to 2,000 angstroms has a sheet resistance of 10² Ω per sheetto 10⁴ Ω per sheet and a light transmittance of 90% or more, andexhibits satisfactory characteristics as the pixel electrode 441.Although the sheet resistance of the ITO film after the first annealingstep is of the order of 10⁵ Ω per sheet to 10⁶ Ω per sheet, the sheetresistance after the second annealing step decreases to the order of 10²Ω per sheet to 10⁴ Ω per sheet.

After forming the ITO film 408 in such a manner, the pixel electrode 441is formed by patterning, as shown in FIG. 19, and thus a TFT 404 isformed in the pixel region 402. When the TFT 404 is driven by controlsignals supplied through the scanning line Gm, image information fordisplaying is input to the liquid crystal cell encapsulated between thepixel electrode 441 and a counter electrode (not shown in the drawings)from the data line Sn through the TFT 404.

In the Second Embodiment as described above, as a liquid coatingmaterial is applied onto the insulating substrate 410 by a coatingprocess, such as a spin coating process, which is suitable for treatmentof large substrates, to form the ITO film for forming the pixelelectrode 441, the ITO film can be formed by an inexpensive system,without using a large film deposition system provided with a vacuumunit, such as a sputtering system.

In the coating method, the liquid or paste coating material fills up thecontact hole 421B as shown in FIG. 25(B) when it is applied onto theinterlevel insulating film 421. The surface shape of the resulting pixelelectrode 441 is only slightly affected by the unevenness of the layersthereunder. As a result, a flat pixel electrode 441 (conductive film)with no surface steps can be formed, rubbing can be stably achieved, andthe occurrence of reverse-tilt domains can be prevented. According tothe Second Embodiment, the display quality is improved.

In contrast, when the pixel electrode is formed by an ITO sputteringfilm 450 as shown in FIG. 25(A), the resulting ITO sputtering film 450is formed according to the steps of the surface thereunder. Such stepson the ITO sputtering film 450 result in unstable rubbing and theoccurrence of reverse-tilt domains, and thus decrease display quality.Further, because it is difficult to form the ITO sputtering film so thatit fills up the entire contact hole 421B, an opening is formed there.Such an opening also results in unstable rubbing and the occurrence ofreverse-tilt domains. Accordingly, it is useful to form a pixelelectrode 441 by an ITO coating film, as shown in FIG. 25(B).

THIRD EMBODIMENT

FIG. 22 is an enlarged partial plan view of pixel regions formed on anactive matrix substrate for a liquid crystal display device, and FIG. 23is a cross-sectional view taken along section II-II′ of FIG. 22.

In FIGS. 22 and 23, differences between the thin film deviceconfiguration on the active matrix substrate 401 for the liquid crystaldisplay device in accordance with the Third Embodiment and the thin filmdevice configuration on the active matrix substrate 400 for the liquidcrystal display device in accordance with the Second Embodiment are asfollows.

The Third Embodiment employs a double-layer-structure interlevelinsulating film including a lower interlevel insulating film 421 formedon a gate electrode 415 and an upper interlevel insulating film 422formed on the lower interlevel insulating film 421. A source electrode431 is therefore formed on the lower interlevel insulating film 421 andis electrically connected to a source region 414 through a contact hole421A in the lower interlevel insulating film 421.

On the other hand, a pixel electrode is formed on the upper interlevelinsulating film 422, and is electrically connected to a drain region 416through a contact hole 422A in the upper interlevel insulating film 422and the lower interlevel insulating film 421. Because the pixelelectrode 441 and the source electrode 431 are formed on differentlayers from each other, these electrodes do not short-circuit eachother.

In the Third Embodiment, as shown in FIG. 22, two peripheral sides 441Aand 441B, parallel to data lines Sn and Sn+1, respectively, of the pixelelectrode 441 in each pixel region 402 lie above the data lines Sn andSn+1. Further two peripheral sides 441C and 441D, parallel to scanninglines Gm and Gm+1, respectively, of the pixel electrode 441 lie abovethe scanning lines Gm and Gm+1. In other words, a part of the pixelelectrode 441 is formed on the data lines Sn and Sn+1 and the scanninglines Gm and Gm+1. No gap is therefore formed between the fourperipheral sides 441A to 441D and the data lines Sn and Sn+1 or thescanning lines Gm and Gm+1 in the plan view. As a result, the data linesSn and Sn+1 and the scanning lines Gm and Gm+1 function as a blackmatrix, and high quality display can be achieved without providingadditional steps for forming a black matrix layer.

The manufacturing process of such an active matrix substrate 401 alsoinclude the steps shown in FIGS. 20(A) to 20(D) for the SecondEmbodiment. The following steps after the steps shown in FIGS. 20(A) to20(D) will be described with reference to FIGS. 24(A) to 24(D).

As shown in FIG. 24(A), after forming a source region 414, a drainregion 416, a channel region 417, a gate region 413 and a gate electrode415, a lower interlevel insulating film 421 composed of a silicon oxidefilm is formed by a CVD or PVD process.

Next, as shown in FIG. 24(B), a contact hole 421A is formed at aposition of the lower interlevel insulating film 421, corresponding tothe source region 414. An aluminum film is formed by a sputteringprocess and then is patterned to form a source electrode 431 and datalines Sn, Sn+1 . . . .

Next, as shown in FIG. 24(C), an upper interlevel insulating film 422composed of a silicon oxide film is formed on the lower interlevelinsulating film 421 by a CVD or PVD process. A contact hole 422A isformed at positions of the lower interlevel insulating film 421 and theupper interlevel insulating film 422, corresponding to the drain region416.

Next, as shown in FIG. 24(D), an ITO film 409 is formed by coating onthe entire surface of the interlevel insulating film 422.

The coating film can be also formed with various liquid and pastecoating materials as in the First and Second Embodiments. Among thesecoating materials, liquid materials are applicable to a dipping or spincoating process, and paste materials are applicable to a screen printingprocess.

In the Third Embodiment, the resulting ITO coating film 409 is subjectedto first and second annealing processes as described above to decreaseits sheet resistance.

Then, the ITO film 409 is patterned to form a pixel electrode 441 asshown in FIG. 23. As described with reference to FIG. 22, in each pixelregion 2, the ITO film 409 is patterned such that the four peripheralsides 441A to 441D of the pixel electrode 441 lie above the data linesSn and Sn+1 and the scanning lines Gm and Gm+1. As the data lines andthe scanning lines are generally formed of a metal film, these datalines and scanning lines can be used as a black matrix. As a result,high quality display can be achieved without further steps.

Further, the pixel region 441 is expanded as much as possible so as tooverlap with the data lines and the scanning lines, hence the pixelregion 402 has a high aperture ratio. The display quality is furtherimproved thereby.

In the Third Embodiment, because the ITO film for forming the pixelelectrode 441 is formed on the insulating substrate 410 by a spincoating process (coating film deposition method) which is suitable fortreatment of a large substrate, using a liquid coating material, thepixel electrode 441 has, as shown in FIG. 10(B), a large thickness at anindented portion of the lower layer and a small thickness at aprotruding portion of the lower layer. As a result, unevenness due tothe data lines is not reflected on the surface of the pixel electrode441. The formation of a flat pixel electrode 441 without surface stepscan stabilize rubbing and prevent the occurrence of reverse-tiltdomains. Such advantages hold on the upper layer side of the scanninglines. The present invention therefore improves display quality.

Further, because a liquid coating material is applied onto theinsulating substrate 410 by a spin coating process, the ITO film forforming the pixel electrode 441 can be formed by an inexpensive filmcoating system, differing from a sputtering process requiring a largefilm deposition system provided with a vacuum unit.

Additionally, the coating method has excellent characteristics forcovering steps, hence large unevenness of the contact holes 421A and422A in the lower and upper interlevel insulating films 421 and 422 doesnot affect the surface shape of the pixel electrode 441 (ITO film).Because the two interlevel insulating films, that is, the lowerinterlevel insulating film 421 and the upper interlevel insulating film422 are formed, a flat pixel electrode 441 without surface steps can beformed regardless of large unevenness due to the contact holes 421A and422A. In such a configuration, the pixel electrode 441 is directlyconnected to the drain region 416 and no repeater electrode (via)electrically connected to the drain region 416 is formed between thelower interlevel insulating film 421 and the upper interlevel insulatingfilm 422, resulting in simplified production steps.

In the formation of the pixel electrode in the Third Embodiment,although a spin coating process is employed to form the ITO film using aliquid coating material, the ITO film can be formed by a printingprocess using a paste coating material. As the paste coating materialcan also be applicable to a screen printing process, a paste coatingmaterial is applied onto only the region forming the pixel electrode441, followed by drying and annealing, and the printed region can beused as the pixel electrode 441 without further steps. Becausepatterning of the ITO by an etching process is not required in thiscase, the production costs can be drastically decreased.

In the Second and Third Embodiments, coplanar-type TFTs are exemplified,in which the surface shape of the pixel electrode 441 is greatlyaffected by the contact holes in the interlevel insulating film. Whenthe present invention is applied to the formation of a pixel electrodeon a lower layer having unevenness in a reverse stagger-type TFT, theeffect of such unevenness on the surface shape of the pixel electrodecan be removed.

FOURTH EMBODIMENT

FIG. 26 is a cross-sectional view taken along section II-II′ of FIG. 22,showing a configuration according to the Fourth Embodiment which isdifferent from that in FIG. 23.

The Fourth Embodiment also employs two interlevel insulating films 420composed of a lower interlevel insulating film 421 and an upperinterlevel insulating film 422 deposited on the lower interlevelinsulating film 421.

The configuration shown in FIG. 26 is different from the configurationin FIG. 23 in that the pixel electrode 441 has a double layer structureconsisting of an ITO sputtering film 446 (conductive sputtering film)formed on the upper interlevel insulating film 422 by a sputteringprocess, and an ITO coating film 447 (conductive transparent coatingfilm) formed on the ITO sputtering film 446.

The ITO coating film 447 is therefore electrically connected to thedrain region 416 through the ITO sputtering film 446 lying thereunder.Because the ITO sputtering film 446 and the ITO coating film 447 aresimultaneously pattern-formed as described below, these have a commonforming region.

Because other portions are the same as those in FIG. 23, the sameidentification numbers are used without detailed description.

The planar layout of the configuration of the Fourth Embodiment is thesame as that of the Third Embodiment, shown in FIG. 22, and thus datalines Sn, Sn+1. . . and scanning lines Gm, Gm+1. . . function as a blackmatrix. As a result, high quality display can be achieved withoutincreasing steps.

In the Third Embodiment, the ITO coating film 447 in contact with thedrain region 416 tends to have a higher contact resistance compared tothe ITO sputtering film. In the Fourth Embodiment, the ITO coating film447 is electrically connected to the drain region 416 through the ITOsputtering film 446, and such a configuration does not cause a highcontact resistance.

A method for making such an active matrix substrate 401 will now bedescribed with reference to FIGS. 27(A) to 27(E) and FIGS. 28(A) to28(E). Because the FIGS. 27(A) to 27(E) are the same as FIGS. 20(A) to20(D) and FIG. 24(A) for the steps of the Third Embodiment,respectively, the description is omitted. Also, the FIGS. 28(B) and28(C) are the same as FIGS. 24(B) and 24(C), respectively, for the stepsof the Third Embodiment.

FIG. 28(A) shows a resist pattern-forming step before the step in FIG.28(B). In order to form the source electrode 431 and the source lineshown in FIG. 28(B), an aluminum film 460 is formed by a sputteringprocess in FIG. 28(A). A patterned resist mask 461 is formed on thealuminum film 460. The source electrode 431 and the data line, as shownin FIG. 28(B), are formed by etching the aluminum film 460 using theresist film 461.

Next, as shown in FIG. 28(C), the upper interlevel insulating film 422composed of a silicon oxide film is deposited on the lower interlevelinsulating film 421 by a CVD or PVD process. After ion implantation andforming the interlevel insulating films, the substrate is annealed in agiven thermal environment at 350° C. or less for several tens of minutesto several hours to activate the implanted ions and to bake theinterlevel insulating film 420 (the lower interlevel insulating film 421and the upper interlevel insulating film 422). A contact hole 422A isformed at positions, corresponding to the drain region 416, in the lowerinterlevel insulating film 421 and the upper interlevel insulating film422.

Next, as shown in FIG. 28(D), an ITO sputtering film 446 (conductivesputtering film) is formed on the entire interlevel insulating film 420composed of the lower interlevel insulating film 421 and the upperinterlevel insulating film 422 by a sputtering process.

Next, as shown in FIG. 28(E), an ITO coating film 447 (conductivetransparent coating film) is formed on the ITO sputtering film 446.

The ITO coating film 447 can be formed under the same process conditionsas in the First to Third Embodiments. The liquid or paste coating filmapplied on the top face in the Fourth Embodiment is annealed in anannealing chamber after the solvent is removed by drying. The coatingfilm is annealed or fired at a temperature of 250° C. to 500° C. andpreferably 250° C. to 400° C. for 30 minutes to 60 minutes in air or anoxygen-containing or nonreducing atmosphere, and then annealed at atemperature of 200° C. or more and preferably 200° C. to 350° C. for 30minutes to 60 minutes in a hydrogen-containing atmosphere. Thetemperature of the second annealing step is set to be lower than that ofthe first annealing step to prevent thermal degradation of the coatingfilm stabilized in the first annealing step. By such annealing steps,organic components are removed, and the coating film is converted to amixed film (ITO coating film 447) of indium oxide and tin oxide. As aresult, the ITO coating film 447 with a thickness of approximately 500angstroms to 2,000 angstroms has a sheet resistance of 10²Ω per sheet to10⁴Ω per sheet and a light transmittance of 90% or more, and this andthe ITO sputtering film 446 can form a pixel electrode 441 exhibitingsatisfactory characteristics.

Next, the insulating substrate 410 is maintained in the nonreductiveatmosphere used in the second annealing step or a nonoxidativeatmosphere such as a gaseous nitrogen atmosphere until the substratetemperature decreases to 200° C. or less, and taken out to open air fromthe annealing chamber when the substrate temperature reaches 200° C. orless. When the insulating substrate 410 is exposed to open air after thetemperature reached 200° C. or less, the coating film having a decreasedresistance by the thermal reduction during the second annealing step isprevented from reoxidation and thus the ITO coating film 447 has a lowsheet resistance. It is more preferable that the temperature when theinsulating substrate 410 is taken but from the annealing chamber to openair be 100° C. or less in order to prevent reoxidation of the ITOcoating film 447. Because the specific resistance of the ITO coatingfilm 447 decreases as oxygen defects in the film increase, reoxidationof the ITO coating film 447 due to oxygen in air increases the specificresistance.

After forming the ITO sputtering film 446 and the ITO coating film 447in such a manner, a resist film 462 is formed, and these films arecollectively patterned with an etching solution, such as aqua regia or aHBr solution, or by dry etching using CH₄ or the like, to form the pixelelectrode 441 as shown in FIG. 26. A TFT is thereby formed in each pixelelectrode 402. When driving the TFT in response to a control signalsupplied through the scanning line Gm, image information is input intothe liquid crystal encapsulated between the pixel electrode 441 and thecounter electrode (not shown in the drawing) from the data line Snthrough the TFT to display a given image.

In this embodiment, the ITO coating film 447 is used to form the pixelelectrode 441. Because the film deposition by coating exhibits excellentcharacteristics for covering the steps, a liquid or paste coatingmaterial to form the ITO coating film 447 can satisfactorily compensateunevenness on the surface of the ITO sputtering film 446 caused by thecontact hole 422. Further, the coating material is coated such that theITO coating film 447 has a large thickness at an indented portion and asmall thickness at a protruded portion. Unevenness due to the data line431 does not therefore replicate the surface of the pixel electrode 441.The same relationship holds in the upper layer of the scanning line 415.Accordingly, a pixel electrode 441 having a flat surface without stepscan be formed, resulting in stable rubbing and prevention of theoccurrence of reverse-tilt domains. The present invention thereforeimproves image quality.

In contrast, when forming the pixel electrode by only an ITO sputteringfilm 446 as shown in FIG. 39A, the ITO sputtering film 446 is replicatedby the steps on the surface on which the ITO sputtering film 446 isformed. The steps formed on the surface of the ITO sputtering film 446cause unstable rubbing and the occurrence of reverse-tilt domains, andthus deteriorate display quality. Further, it is difficult to form theITO sputtering film 446 so as to fill the entire contact hole 422A,hence an opening is inevitably formed. Such an opening also causesunstable rubbing and the occurrence of reverse-tilt domains. Theformation of the ITO coating film 447 therefore is useful.

As shown in the Fourth Embodiment, when the interlevel insulating film420 has a double layer structure for the purpose of forming the pixelelectrode 441 and the source electrode 431 on different interlayers, theaspect ratio of the contact hole 422A increases; however, the ITOcoating film 447 can form a flat pixel electrode 441 regardless of this.

The ITO sputtering film 446 has a trend of poor adhesion to a resistmask compared to the ITO coating film 447; however, the resist mask 462is formed on the ITO coating film 447 in this embodiment, and accuracyof patterning is not deteriorated. A pixel electrode 441 having a highdefinition pattern can therefore be formed.

FIFTH EMBODIMENT

FIG. 29 is an enlarged plan view of a part of a pixel region formed onan active matrix substrate for a liquid crystal display in accordancewith the present invention, and FIG. 30 is a cross-sectional view takenalong section III-III′ of FIG. 29. In the Fifth Embodiment, parts havingthe same function as in the Fourth Embodiment are referred to with thesame identification numbers, and a detailed description thereof withreference to drawings is omitted. In FIG. 29, the active matrixsubstrate 401 for a liquid crystal display in accordance with the FifthEmbodiment is also provided with a plurality of pixel electrode regions402 formed by data lines 431 and scanning lines 415 on an insulatingsubstrate 410, and a TFT is formed on each of the pixel electroderegions 402.

The planar layout in the Fifth Embodiment other than the ITO sputteringfilm is identical to the configuration shown in FIG. 22 for illustratingthe Third and Fourth Embodiments, hence data lines Sn, Sn+1. . . andscanning lines Gm, Gm+1. . . function as a black matrix. High qualityimage display therefore can be achieved without additional steps.

Because in the Fifth Embodiment an ITO sputtering film 456 and an ITOcoating film 457 are separately patterned as described below in contrastto the Fourth Embodiment, their regional areas are different from eachother. That is, the regional area of the ITO coating film 457 is largerthan the regional area of the ITO sputtering film 456.

When forming the ITO coating film and the ITO sputtering film on acommon region as in the Fourth Embodiment, these two ITO films can besimultaneously patterned. The resist mask is formed only on the ITOcoating film having excellent adhesiveness to the resist mask, and isnot formed on the ITO sputtering film having poor adhesiveness to theresist mask. High definition patterning can therefore be achieved.

In contrast, in the Fifth Embodiment, a resist mask must be formed alsoon the surface of the ITO sputtering film. When the regional area of theITO coating film is larger than the regional area of the ITO sputteringfilm, the accuracy of patterning of the ITO coating film havingexcellent adhesiveness to the resist mask determine a final pattern.Hence high definition patterning can be achieved even if the ITOsputtering film has poor adhesiveness to the resist mask.

The steps shown in FIGS. 31(A) to 31(C) for a manufacturing method ofsuch an active matrix substrate is similar to FIGS. 27(A) to 27(E) forthe Fourth Embodiment. Thus, only the steps shown in FIGS. 31(D) to31(F) will now be described.

In FIG. 31(C), an upper interlevel insulating film 422 composed of asilicon oxide film is formed on a lower interlevel insulating film 421,and then a contact hole 422A is formed.

Next, as shown in FIG. 31(D), an ITO film 456 (conductive sputteringfilm) is formed by a sputtering process on the entire surface of theinterlevel insulating film 420 composed of the lower interlevelinsulating film 421 and the upper interlevel insulating film 422. Thesesteps is also identical to the Fourth Embodiment.

In the Fifth Embodiment, however, only the ITO sputtering film 456 ispatterned with an etching solution, such as aqua regia or a HBrsolution, or by dry etching using CH₄ or the like. After forming the ITOsputtering film 456, a resist mask 464 is formed as shown FIG. 31(D) andis patterned. The ITO sputtering film 456 is etched using the resistmask 464 such that the ITO sputtering film 456 remains in a region whichis narrower than the region of a pixel electrode 441 to be formed. AnITO coating film (conductive transparent coating film) is formed on thetop face of the ITO sputtering film 456. The coating materials describedin the above-mentioned Embodiments can be used for forming the ITOcoating film 457.

After forming the ITO coating film 457 in such a manner, a resist mask462 is formed as shown in FIG. 31(F) and is patterned with an etchingsolution, such as aqua regia or a HBr solution, or by dry etching usingCH₄ or the like to form a pixel electrode 441 as shown in FIG. 30.

The configuration in the Fifth Embodiment has similar advantages to thatin the Fourth Embodiment. In particular, although the ITO coating film457 in contact with a drain region has a higher contact resistance thanthe ITO sputtering film, the ITO coating film 457 in the FifthEmbodiment is electrically connected to the drain region 416 through theITO sputtering film 456 to cancel such a high contact resistance.Because the ITO sputtering film can be thin, it can be etched within ashort time without preventing patterning, regardless of pooradhesiveness to the resist mask 464. Because the ITO coating film 457having high accuracy for patterning determines final accuracy of thepixel electrode 40 for patterning, high accuracy patterning can beachieved.

SIXTH EMBODIMENT

FIG. 32 is an enlarged plan view of a part of a pixel region formed onan active matrix substrate for a liquid crystal display in accordancewith the present invention, and FIG. 33 is a cross-sectional view takenalong section IV-IV′ of FIG. 30.

The arrangement in the Sixth Embodiment is characterized in that a pixelelectrode 441 is composed of an ITO coating film (conductive transparentcoating film) 468 formed by coating on an upper interlevel insulatingfilm 422, and the ITO coating film 468 is electrically connected to arepeater electrode 466 composed of an aluminum film formed on a lowerinterlevel insulating film 421 by a sputtering process through a contacthole 422A in the upper interlevel insulating film 422. The repeaterelectrode 466 is electrically connected to a drain region 416 through acontact hole 421B in the lower interlevel insulating film 421. As aresult, the pixel electrode 441 is electrically connected to the drainelectrode 416 through the repeater electrode 466 lying thereunder.

Because the repeater electrode 466 composed of an aluminum film does nothave light transmitting characteristics, the region for forming it islimited to the interior and periphery of the contact hole 421 so as notto decrease the aperture ratio.

The steps shown in FIGS. 27(A) to 27(E) for the Fourth Embodiment can beemployed for the manufacturing method of such an active matrix substrate401. The succeeding steps after the step in FIG. 27(E) will now bedescribed with reference to FIGS. 34(A) to 34(D).

As shown FIG. 34(A), after contact holes 421A and 421B are formed atpositions corresponding to a source region 414 and a drain region 416,respectively, in the lower interlevel insulating film 421, an aluminumfilm 460 (conductive sputtering film or metal film) is formed bysputtering to form a source electrode 431 and data lines. Next, a resistmask 470 is formed and the aluminum film 460 is patterned using theresist mask 470. As a result, as shown in FIG. 34(B), the sourceelectrode 431, the data lines and the repeater electrode 466 aresimultaneously formed.

Next, as shown in FIG. 34(C), an upper interlevel insulating film 422 ofa silicon oxide film is formed on the surface of the lower interlevelinsulating film 421 by a CVD or PVD process. A contact hole 422A isformed at a position corresponding to the repeater electrode 466 (aposition corresponding to the drain region 416) in the upper interlevelinsulating film 422.

Next, as shown in FIG. 34(D), an ITO coating film 468 (conductivetransparent coating film) is formed on the entire interlevel insulatingfilm 420 consisting of the lower interlevel insulating film 421 and theupper interlevel insulating film 422.

The coating material described in the above-mentioned embodiments can beused for forming the ITO coating film 468.

After forming the ITO film 468 in such a manner, a resist mask 462 isformed and patterned to form a pixel electrode 441 as shown in FIG. 33.

As shown in FIG. 32, data lines Sn, Sn+1. . . and scanning lines Gm,Gm+1. . . function as a black matrix. Further, the aperture ratio of thepixel region 402 can be increased and a pixel electrode 441 having aflat surface without steps can be formed. Hence rubbing is stabilizedand the occurrence of reverse-tilt domains can be prevented.

Although the pixel electrode 441 composed of the ITO coating film 468has a higher contact resistance with the drain region 416 (silicon film)than the ITO sputtering film, the ITO coating film 468 in the SixthEmbodiment is electrically connected to the drain region 416 through therepeater electrode 466 composed of the aluminum film formed bysputtering to counter such a high contact resistance.

Although aluminum is used for the repeater electrode 466 in thisembodiment, use of a dual layer film composed of aluminum and a highmelting point metal can further decrease the contact resistance with theITO coating film 468. The high melting point metal, such as tungsten ormolybdenum, is difficult to oxidize as compared to aluminum, and even ifit comes into contact with the ITO coating film 468 containing a largeamount of oxygen, no oxidation occurs. The contact resistance betweenthe repeater electrode 466 and the ITO coating film 468 can therefore bereduced.

SEVENTH EMBODIMENT

FIG. 35 is an enlarged plan view of a part of a pixel region formed onan active matrix substrate for a liquid crystal display in accordancewith the present invention, and FIG. 36 is a cross-sectional view takenalong section V-V′ of FIG. 35.

The Seventh Embodiment includes a modified configuration of SecondEmbodiment shown in FIG. 18 and FIG. 19, in which a repeater electrode480 achieves electrical connection between an ITO coating film 441 and adrain region 416.

In FIG. 35, an active matrix substrate 401 in accordance with theSeventh Embodiment is also provided with a plurality of pixel regions402 formed by data lines 431 and scanning lines 416 on an insulatingsubstrate 410, and each of the pixel regions 402 is provided with a TFT(a nonlinear element for pixel switching). If only planarization of thepixel electrode and reduction of the contact resistance are intended,the following configuration is available.

As shown in FIG. 36, in the Seventh Embodiment, an interlevel insulatingfilm 421 is composed of one silicon oxide layer.

The pixel electrode 441 composed of the ITO coating film is formed onthe top face of the repeater electrode 480 composed of an aluminum film(conductive sputtering film or metal film) which is formed on theinterlevel insulating film 421 by a sputtering process. The pixelelectrode 441 is therefore electrically connected to the drain region416 through the repeater electrode 480. Because the repeater electrode480 composed of an aluminum film does not have light transmittingcharacteristics, the region for forming it is limited to the interiorand periphery of the contact hole 421B.

Because the pixel electrode 441 and the source electrode 431 are formedbetween two common layers in the Seventh Embodiment, such that these twoelectrodes are not short-circuited (refer to FIG. 35 and FIG. 36).

Such an active matrix substrate 401 is manufactured according to thesteps shown in FIGS. 27(A) to 27(B) for the Fourth Embodiment. Thesucceeding steps after FIG. 27(E) will now be described with referenceto FIGS. 37(A) to 37(C).

As shown in FIG. 37(A), contact holes 421A and 421B are formed atpositions corresponding to a source region 414 and a drain region 416,respectively, in the interlevel insulating film 421. After forming bysputtering an aluminum film 460 for forming the source electrode 431 anddata lines, a resist mask 470 is formed. Next, the aluminum film 460 ispatterned using the resist mask 470 to form the source electrode 431,the data lines and the repeater electrode 480 as shown in FIG. 37(B).

Next, as shown in FIG. 37(C), an ITO coating film 482 (conductivetransparent electrode) is formed on the entire top face of theinterlevel insulating film 421. The coating films used in theabove-mentioned embodiments can be used for forming the ITO coating film482.

After forming the ITO coating film 482 in such a manner, a resist mask484 is formed and the ITO coating film 482 is patterned using the resistmask 484 to form a pixel electrode 441 as shown in FIG. 36.

Accordingly, a pixel electrode 441 having a flat surface without stepscan be formed, resulting in stable rubbing and prevention of theoccurrence of a reverse-tilt domain. Further, an increase in the contactresistance between the pixel electrode composed of the ITO coating filmformed by a coating process and the drain region 416 can be prevented.

The present invention is not limited the above-described embodiments andcan include various modifications within the scope of the presentinvention.

For instance, in the Sixth and Seventh Embodiments, the repeaterelectrodes 466 and 480, the source electrode 431 and the data lines aresimultaneously formed of the common metal film (aluminum film). Instead,when the interlevel insulating film 420 includes a lower interlevelinsulating film 421 and an upper interlevel insulating film 422, boththe pixel electrode 441 composed of the ITO film by a coating processand the repeater electrode 486 composed of a conductive sputtering filmmay be formed on the upper insulating film 422. Such a configuration canextend the region forming the pixel electrode 441, differing from theSixth Embodiment, and thus data lines and scanning lines function as ablack matrix. Because the repeating electrode 486 (conductive sputteringfilm) and the source electrode 431 are formed by different steps, thematerial for the repeating electrode 486 may be the same as or differentfrom the material for the source electrode 431.

In both the Sixth and Seventh Embodiments, although planar-type TFTs aredescribed in which the contact holes in the interlevel insulating filmsgreatly affect the surface shapes of the pixel electrodes, the presentinvention can also be applied to a reverse stagger-type TFT. When thepixel electrode is forced to be formed on an uneven surface, the surfaceof the pixel electrode formed of a conductive transparent coating filmby a coating process as in the present invention is not affected by suchunevenness.

For example, an ITO coating film is used as the pixel electrode 441 in areverse stagger-type TFT shown in FIG. 38(B) for the purpose ofplanarization of the surface of the pixel electrode 441. In the TFTshown in FIG. 38(B), a protective underlayer 411, a gate electrode 415,a gate insulating film 413, an intrinsic amorphous silicon film forminga channel region 417 and an insulating film 490 for protecting thechannel are deposited in that order on an insulating substrate 410.Source and drain regions 414 and 416 composed of a high concentrationn-type amorphous silicon film are formed on both sides of the insulatingfilm 490 for protecting the channel, and a source electrode 431 and arepeater electrode 492 composed of a sputtering film such as chromium,aluminum or titanium are formed on the source and drain regions 414 and416. Further, an interlevel insulating film 494 and a pixel electrode441 are formed thereon. Because the pixel electrode 331 is composed ofan ITO coating film, it has a flat surface. The pixel electrode 441 iselectrically connected to the repeater electrode 496 through a contacthole in the interlevel insulating film 441. Because the pixel electrode441 is electrically connected to the drain region 416 through therepeater electrode 496 composed of the sputtering film, the problem ofhigh contact resistance between the pixel electrode 441 composed of theITO coating film and the drain region 416 (silicon film) can be solved.Because the pixel electrode 441 and the source electrode 431 arearranged between different layers, these electrode does notshort-circuit. As a result, the pixel electrode 441 can be formed in awide range so as to cover the data lines and the scanning lines (notshown in the drawing). Hence the data lines and the scanning linesfunctions as a black matrix and the aperture ratio of the pixel regioncan be increased.

Although the ITO coating film for forming the pixel electrode isdeposited with a liquid coating material by a spin coating process, theITO coating film may be deposited using a paste coating material by aprinting process. Further use of the paste coating material enables ascreen printing process, in which the paste coating material is printedonly on the region to form the pixel electrode followed by drying andannealing, and the resulting film can be used as the pixel electrode.Because this case does not require patterning of the ITO film, theproduction costs can be drastically reduced.

Although only the pixel electrode is formed of a coating film in theSecond to Seventh Embodiments, any one of an insulating layer, aconductive layer and a semiconductive layer, as well as the pixelelectrode, can be, of course, formed of a coating film, as described inthe First Embodiment.

EIGHTH EMBODIMENT

An electronic device formed of a liquid crystal display device inaccordance with any of the above-mentioned embodiments includes, asshown in FIG. 40, a display information source 1000, a displayinformation processing circuit 1002, a display driving circuit 1004, adisplay panel 1006 such as a liquid crystal panel, a clock generatingcircuit 1008 and an electric power circuit 1010. The display informationsource 1000 includes memories such as ROM and RAM, and a tuning circuitfor tuning and outputting the television signals, and output displayinformation such as video signals based on a clock from the clockgenerating circuit 1008. The display information processing circuit 1002processes and output the display information based on the clock from theclock generating circuit. The display information processing circuit1002 may include, for example, an amplification and polarity inversioncircuit, a circuit with parallel data input, a rotation circuit, a gammacorrection circuit and a clamping circuit. The display driving circuit1004 includes a scanning line driving circuit and a data line drivingcircuit and drives to display the liquid crystal panel 1006. Theelectric power circuit 1010 supplies electric power to theabove-mentioned circuits.

Examples of electronic devices having such a configuration includeliquid crystal projectors as shown in FIG. 41, personal computers (PCs)as shown in FIG. 42, and engineering work stations (EWSs) responding tomultimedia pagers as shown in FIG. 43 and portable phones, wordprocessors, televisions, view finder-type and monitor-type videotaperecorders, electronic notebooks, electronic desktop calculators, carnavigation systems, POS terminals, and apparatuses provided with touchpanels.

The liquid crystal projector shown in FIG. 41 is a projectiontype-projector using a transparent liquid crystal panel as a light valveand includes, for example, a three-plate prism-type optical system.

In the projector 1100 shown in FIG. 41, projection light emerging from alamp unit 1102 provided with a white light source is divided into threeprimary colors, R, G and B by a plurality of mirrors 1106 and twodichroic mirrors 1108 in a light guide 1104, and the three primarycolors are introduced to three color liquid crystal panels 1110R, 1110Gand 1110B for displaying their respective colors. The light beamsmodulated by the liquid crystal panels 1110R, 1110G and 1110B areincident on a dichroic prism 1112 from three directions. In the dichroicprism 1112, as the red R and blue B light beams are reflected by 90°,whereas the green G light beam travels straight, images of these colorsare combined and, thus, a color image is projected on a screen or thelike through a projection lens.

The personal computer 1200 shown in FIG. 42 includes a main body 1204provided with a key board 1202 and a liquid crystal display screen 1206.

The pager 1300 shown in FIG. 43 includes a liquid crystal display board1304, a light guide 1306 provided with a back light 1306 a, a circuitboard 1308, a first shield plate 1310 and a second shield plate 1312,two elastic conductors 1314 and 1316 and a film carrier tape 1318, whichare provided in a metallic frame 1302. The two elastic conductors 1314and 1316 and the film carrier tape 1318 are provided for connecting theliquid crystal display board 1304 to the circuit board 1308.

The liquid crystal display board 1304 is composed of a liquid crystalencapsulated between two transparent substrates 1304 a and 1304 b andforms at least a dot-matrix liquid crystal panel. One of the transparentsubstrates may be provided with a driving circuit 1004 shown in FIG. 40,and additionally, a display information processing circuit 1002.Circuits not mounted in the liquid crystal display board 1304 can bemounted in the circuit board 1308 shown in FIG. 43 as an externalcircuit of the liquid crystal display board.

The pager configuration shown in FIG. 43 further requires a circuitboard 1308, as well as the liquid crystal display board 1304, and when aliquid crystal display device is used as one unit in an electronicdevice and when a display driving circuit is mounted onto a transparentboard, the minimum unit of the liquid crystal display device is theliquid crystal display board 1304. Alternatively, the liquid crystaldisplay board 1305 fixed into the metallic frame 1302 can be used as aliquid crystal display device which is a part of an electronic device.Further a back-light-type liquid crystal display device can be formed byassembling the liquid crystal display board 1304, and a light guide 1306provided with a back light 1306 a into the metallic frame 1302. Instead,as shown in FIG. 44, a tape carrier package (TCP) 1320, in which an ICchip 1324 is packaged onto a polyimide tape 1322 provided with ametallic conductive film, may be connected to one of the two transparentsubstrates 1304 a and 1304 b of the liquid crystal display board 1304 tobe used as a liquid crystal display device as a part of the electronicdevice.

1. A method of forming a device, the method comprising: applying a firstsolution to form a first applied film over a portion of a substrate, thefirst applied film being patterned, the first solution including a firstsolvent and a first solute; heating the first applied film at atemperature ranging from 250° C. to 500° C. to form a first film overthe portion, the first solvent being evaporated during a period in whichthe heating of the first applied film is carried out; applying a secondsolution to form a second applied film over the portion of thesubstrate, the second applied film being patterned, the second solutionincluding a second solvent and a second solute; heating the secondapplied film at a temperature ranging from 250° C. to 500° C. to form asecond film over the portion, the second solvent being evaporated duringa period in which the heating of the second applied film is carried out;applying a dispersion liquid to form a third applied film over theportion of the substrate, the dispersion liquid including a dispersionmedium and a dispersoid, the dispersoid being a metal particle with asize of 80 to 100 angstroms; and heating the third applied film at atemperature ranging from 250° C. to 500° C. to form a third film overthe portion.
 2. The method of forming a device according to claim 1, thefirst solvent being a terpineol.
 3. The method of forming a deviceaccording to claim 1, the first solute being a semiconductor material.4. A method of forming a device, the method comprising: applying a firstsolution to form a first applied film over a portion of a substrate, thefirst applied film being patterned, the first solution including a firstsolvent and a first solute; heating the first applied film at atemperature ranging from 250° C. to 500° C. to form a first film overthe portion, the first solvent being evaporated during a period in whichthe heating of the first applied film is carried out; applying a secondsolution to form a second applied film over the portion of thesubstrate, the second applied film being patterned, the second solutionincluding a second solvent and a second solute; heating the secondapplied film at a temperature ranging from 250° C. to 500°C. to form asecond film over the portion, the second solvent being evaporated duringa period in which the heating of the second applied film is carried out;applying a dispersion liquid to form a third applied film over theportion of the substrate, the dispersion liquid including a dispersionmedium and a dispersoid, the dispersoid being an Al particle; andheating the third applied film at a temperature ranging from 250° C. to500° C. to form a third film over the portion.
 5. A method of forming adevice, the method comprising: applying a first solution to form a firstapplied film over a portion of a substrate, the first applied film beingpatterned, the first solution including a first solvent and a firstsolute; heating the first applied film at a temperature ranging from250° C. to 500° C. to form a first film over the portion, the firstsolvent being evaporated during a period in which the heating of thefirst applied film is carried out; applying a second solution to form asecond applied film over the portion of the substrate, the secondapplied film being patterned, the second solution including a secondsolvent and a second solute; heating the second applied film at atemperature ranging from 250° C. to 500° C. to form a second film overthe portion, the second solvent being evaporated during a period inwhich the heating of the second applied film is carried out; applying adispersion liquid to form a third applied film over the portion of thesubstrate, the dispersion liquid including a dispersion medium and adispersoid, the dispersoid being an Ag article; and heating the thirdapplied film at a temperature ranging from 250° C. to 500° C. to form athird film over the portion.
 6. A method of forming a device, the methodcomprising: applying a first solution to form a first applied film overa portion of a substrate, the first applied film being patterned, thefirst solution being patterned, the first solution including a firstsolvent and a first solute; heating the first applied film at atemperature ranging from 250° C. to 500° C. to form a first film overthe portion, the first solvent being evaporated during a period in whichthe heating of the first applied film is carried out; applying a secondsolution to form a second applied film over the portion of thesubstrate, the second applied film being patterned, the second solutionincluding a second solvent and a second solute; heating the secondapplied film at a temperature ranging from 250° C. to 500° C. to form asecond film over the portion, the second solvent being evaporated duringa period in which the heating of the second applied film is carried out;applying a dispersion liquid to form a third applied film over theportion of the substrate, the dispersion liquid including a dispersionmedium and a dispersoid, the dispersoid being an Cu particle; andheating the third applied film at a temperature ranging from 250° C. to500° C. to form a third film over the portion.